Your CPU/GPU is overheating. In order for your laptop to hold a temperature under 100C, it will decrease your CPU clock (which causes stuttering). Here are the steps I did to prevent it from overheating and how I removed stuttering from games like GTA 5, Red Dead Redemption 2 and Apex Legends :

1. Remove any overclocks on your GPU/CPU.

Overclocking gets you small improvements in games but forces more power drawing which generates heat.

2. Undervolt your CPU. 

Download Intel Xtreme Tuning Utility (Intel XTU for short) from the official Intel website https://downloadcenter.intel.com/product/66427/Intel-Extreme-Tuning-Utility-Intel-XTU- .  Go through the setup process (you may need to restart your computer). Open the app and you will be greeted with this screen : 

Some settings may look different to you. All you need to do is change the Core Voltage Offset setting from 0.000V to something ranging from -0.050V to -0.150V. Try each value in between and go down each -0.010V (ex from -0.050V to -0.060V then to -0.070V and so on). If you go down too much, usually when the CPU stresses a bit more than usual your laptop may crash (BUT don't worry, Intel XTU has a watchdog service , if it detects an unexpected crash due to a wrong setting). I personally recommend the -0.110V setting as it is a good setting for begginers and it reduces approximately 5C to 15C.  If you feel like you can go lower and your laptop still does overheat you can go lower for example -0.115V / -0.125V and so on. DO NOT CHANGE ANY OTHER SETTING AS IT IS NOT NEEDED AND IT IS FOR ADVANCED USERS.
You can use the small left arrow when you hover on the Core Voltage Offset value to go lower. You can also watch a guide on undervolting on YouTube if you feel like my instructions aren't clear enough. Intel XTU is only available on Intel processors!

3. Disable Intel Turbo Boost Technology / AMD Core Clock Boost Technology.
This one is the most reliable and easiest way to lower your temperatures (you can do it from Windows Control Panel, your BIOS/UEFI or your CPU management app.)

The easiest way is to do it from Windows, as you can change settings on the go, when you need more power for a game you can just change the setting back without restarting your computer. If you want to disable it from BIOS/UEFI, you may find a setting named Intel Turbo Boost Technology/AMD Core Clock Boost and toggle them off. I HIGHLY SUGGEST THE WINDOWS ONE AS IT IS THE EASIEST AND IT IS NOT DANGEROUS FOR BEGINNERS.  I will only include the in-depth guide for the Windows Control Panel, as it is the one I used and the safest one.
Here are the steps :
  Use the Processor Performance Boost Mode setting (located in Control Panel>System and Security>Power Options>(your current power plan) >Change Advanced Power Settings>Processor performance boost mode > On battery & Plugged in and set them to Disabled.
If it's not there don't worry, you can make it appear yourself by doing the following :

1. Press the Windows key + X, right-click on either Command Prompt or PowerShell, and choose run as administrator.
2. Type in the following command (in one line), and press Enter afterwards.

powercfg.exe -attributes sub_processor perfboostmode -attrib_hide

After you’ve made the settings visible, you can find the new option in the Advanced Power Options dialog and follow the steps I presented upper (Disabling Procesor Performance Boost Mode).
*NOTE* : This may impact your gaming performance (you may lose 5-10 FPS average, but won't impact you worse than your CPU overheating/throttling).

4. Lower your graphics settings on the games you are playing (Optional).
The higher graphics settings you use, the higher the impact and stress on your CPU/GPU. High graphics are just eye-candy, lowering your settings won't ruin the game as modern games have low settings that still look good.
5. Enable V-Sync (Optional) to half your refresh rate if you have a display capable of more than 60hz (for example if you have 144hz, you will have approximately 75hz frame rate cap).

I only applied steps 2 and 3 and from 86C-96C I managed to lower my temperatures to 50C on idle and 60C on average while gaming, with a maximum of 67C when the room is hot and I am playing a game on the highest settings. It also removed the stuttering caused by thermal throttling (but not for some games like COD:Warzone as i have only 8GB of RAM) but Red Dead Redemption 2 works flawlessly with 40fps constant, medium-high settings 1080P on an i5-8300H, GTX 1050 4GB and 8GB of RAM.

Your CPU/GPU is overheating. In order for your laptop to hold a temperature under 100C, it will decrease your CPU clock (which causes stuttering). Here are the steps I did to prevent it from overheating and how I removed stuttering from games like GTA 5, Red Dead Redemption 2 and Apex Legends :

1. Remove any overclocks on your GPU/CPU.

Overclocking gets you small improvements in games but forces more power drawing which generates heat.

2. Undervolt your CPU. 

Download Intel Xtreme Tuning Utility (Intel XTU for short) from the official Intel website https://downloadcenter.intel.com/product/66427/Intel-Extreme-Tuning-Utility-Intel-XTU- .  Go through the setup process (you may need to restart your computer). Open the app and you will be greeted with this screen : 

Some settings may look different to you. All you need to do is change the Core Voltage Offset setting from 0.000V to something ranging from -0.050V to -0.150V. Try each value in between and go down each -0.010V (ex from -0.050V to -0.060V then to -0.070V and so on). If you go down too much, usually when the CPU stresses a bit more than usual your laptop may crash (BUT don't worry, Intel XTU has a watchdog service , if it detects an unexpected crash due to a wrong setting). I personally recommend the -0.110V setting as it is a good setting for begginers and it reduces approximately 5C to 15C.  If you feel like you can go lower and your laptop still does overheat you can go lower for example -0.115V / -0.125V and so on. DO NOT CHANGE ANY OTHER SETTING AS IT IS NOT NEEDED AND IT IS FOR ADVANCED USERS.
You can use the small left arrow when you hover on the Core Voltage Offset value to go lower. You can also watch a guide on undervolting on YouTube if you feel like my instructions aren't clear enough. Intel XTU is only available on Intel processors!

3. Disable Intel Turbo Boost Technology / AMD Core Clock Boost Technology.
This one is the most reliable and easiest way to lower your temperatures (you can do it from Windows Control Panel, your BIOS/UEFI or your CPU management app.)

The easiest way is to do it from Windows, as you can change settings on the go, when you need more power for a game you can just change the setting back without restarting your computer. If you want to disable it from BIOS/UEFI, you may find a setting named Intel Turbo Boost Technology/AMD Core Clock Boost and toggle them off. I HIGHLY SUGGEST THE WINDOWS ONE AS IT IS THE EASIEST AND IT IS NOT DANGEROUS FOR BEGINNERS.  I will only include the in-depth guide for the Windows Control Panel, as it is the one I used and the safest one.
Here are the steps :
  Use the Processor Performance Boost Mode setting (located in Control Panel>System and Security>Power Options>(your current power plan) >Change Advanced Power Settings>Processor performance boost mode > On battery & Plugged in and set them to Disabled.
If it's not there don't worry, you can make it appear yourself by doing the following :

1. Press the Windows key + X, right-click on either Command Prompt or PowerShell, and choose run as administrator.
2. Type in the following command (in one line), and press Enter afterwards.

powercfg.exe -attributes sub_processor perfboostmode -attrib_hide

After you’ve made the settings visible, you can find the new option in the Advanced Power Options dialog and follow the steps I presented upper (Disabling Procesor Performance Boost Mode).
*NOTE* : This may impact your gaming performance (you may lose 5-10 FPS average, but won't impact you worse than your CPU overheating/throttling).

4. Lower your graphics settings on the games you are playing (Optional).
The higher graphics settings you use, the higher the impact and stress on your CPU/GPU. High graphics are just eye-candy, lowering your settings won't ruin the game as modern games have low settings that still look good.
5. Enable V-Sync (Optional) to half your refresh rate if you have a display capable of more than 60hz (for example if you have 144hz, you will have approximately 75hz frame rate cap).

I only applied steps 2 and 3 and from 86C-96C I managed to lower my temperatures to 50C on idle and 60C on average while gaming, with a maximum of 67C when the room is hot and I am playing a game on the highest settings. It also removed the stuttering caused by thermal throttling (but not for some games like COD:Warzone as i have only 8GB of RAM) but Red Dead Redemption 2 works flawlessly with 40fps constant, medium-high settings 1080P on an i5-8300H, GTX 1050 4GB and 8GB of RAM.