You don't need a specialized benchmark to do a benchmark, you can use a realtime rendered cutscene, you can do an average over several games. That's how they have been done for like a decade and a half at this point.
Also, I'm not referring specifically to mobile graphics nvidia, but nvidia altogether. Linux laptop gamers make up a very very small amount of total Linux gamers, it is an incredibly small niche of two already small niches, both being Linux and laptop gamers. Yes, of course if you have a limit to the total amount of power, it will lag behind.
I gave you a list of games, start there, my list is also diverse and includes all of those except for vulkan, which if you want, throw doom eternal in there, though as I have already stated vulkan will get a small increase on linux over windows in terms of GPU performance, so that's not really proving anything anyone doesn't already know.
If you want a fair comparison, limit it to 80 watts in windows as well. Remember though that power is NOT EVERYTHING when it comes to GPU performance. All of the games I detailed above are GPU bound games and will be a fair comparison. Just a heads up darktide may or may not have graphical glitches on your system if you are running amd (both operating systems, it is hardware related), I've worked with the devs to fix it in the past but it seems like recently people have been having issues with it again.