

I second disabling Nouveau via blacklist, and I’m unsure if there is similar software for Lenovo, but I use asusctl to force the use of the Nvidia card over the integrated Vega graphics. This could very well be an issue with graphics card switching, so it’s worth looking into.
As for distro recs, while most would probably recommended Linux Mint for beginners, I prefer to recommend Bazzite. It’s Fedora-based, but comes with Nvidia drivers and lots of gaming optimization baked-in.
Thermal Grizzly Kryonaut has worked well for me. A quick Google search shows a standard AMD AM5 CPU IHS is 32×32mm, and the normal recommendation for that is a pea sized dot in the center. Given that you’re talking about a laptop CPU, the exposed die will be significantly smaller. A delidded i7-8700k, for instance, is 9.2x16.7mm, which is only 15% of the area, so you would use roughly 15% of a pea of thermal paste for that die size. Granted, I don’t know the actual die size of an i7-7500U, so take that with a grain of salt.
Here is an iFixIt guide on how to repaste a laptop. Do not forget to remove the old thermal paste (and do so with a lint free cloth)! They recommend using an amount of thermal paste the size of a grain of rice. That seems a little small to me, but then again, I only paste desktop processors. I expect someone else here may have more experience with laptops.