You're going to have to compromise on your expectations. Lenovo's tower desktop machines over the past few years have really shrunk n the "depth" dimension, which influences the length of cards you can install in the available expansion slots. In particular, your real choices for graphics card add-ons is severely limited.
The M720t tower is a VERY SMALL TOWER. Even smaller than the M710t tower, which was reduced a few inches from the "at least decent" M700t tower. Add to that a small power supply of 210W and you're REALLY LIMITED.
The mechanical specs for max dimensions of cards you can use are shown in the PSREF:

That means your graphics card must be under 189mm in length and under 104mm in height.
This was exactly why I recently finally gave up on using an M720t for a friend who wanted me to build a new machine for her. I first looked at the M720t but eventually I ended up going with an M920t which has a somewhat larger interior than that of the M720t, and also has a larger 250W PSU.
For comparison, the mechanical limiations of the slightly larger (but still not terrific) M920t max-size card limitations are: 268mm length and 112mm height. The length is much better but the height is still a bit problematic. However now at least I could use THIS Gigabyte low-profile GTX 1050ti OC card which is 167mm long and 70mm high, and everything would likely be much happier with the 250W PSU in the M920t.
So in these smaller tower cases the best under-75W graphics card you can install is a GTX 1050ti of some kind, and likely you will be forced to settle for something less because the length and height are a problem, along with the 210W PSU limitation. Even though it is a "tower" case you cannot use full-size single-fan cards that are "short" and which really shouldn't be causing a problem even with the 189mm max length limitation in the M920t. For example, I used this single-fan "short" full-size EVGA GTX 1050ti SC card in two M910t towers, and it has a length of 5.7" (144mm) and a height of 4.38" (111.25mm). Although this might have actually fit in the M920t with its max height of 112mm I didn't want to chance it. So I didn't use it in the M920t since I had the additional option of that lower but longer low-profile Gigabyte 1050ti card.
The M720t case is even smaller, and has size limitations in both the length (<189mm) and height (<104mm) dimensions, plus its 210W PSU. You can go from here. You may have to live with a GT1030 variation as the "best you can get" within the constraints of these recent assortment of Lenovo new smaller tower cases.
Gone are the days of the M93p tower, or even the M700t/M800t/M900t where you could pretty much use any graphics card and could even install a standard ATX power supply (with appropriate 24-14 or 24-10 power adapter to the odd connector on Lenovo motherboards). The smaller "depth" of even the M920t cannot hold the standard ATX PSU dimension of 6 11/16" length, and is limited to the Lenovo-supplied PSU (or similar physical sized but larger wattage 3rd-party replacement) with its reduced length of 5 1/2" (maybe standard for "microATC"?)... which is about 1 1/4" shorter in length than a standard ATX PSU. This turns out to be critical inside the case, in order to allow the drive assembly mechanism to swing down and fully close/lock as intended. Ths is impossible with the larger standard ATX PSU, I can attest to, as I was recently disappointed when I tried to replace the smaller Lenovo 250W PSU in the M920t with a standard ATX 600W fanless PSU. So be careful if you shop for a PSU replacement for the M720t, as size REALLY matters here.
I don't have firsthand experience with the GT1030, but that may be your best bet... given the physical limitations and 210W PSU in the M720t.