I have a laptop GPU: GeForce GTX 860M. It’s third class but enough to play lo-poly 3D games, or games set in low graphics quality (as proven with this one in windowed mode). The flickering issue doesn’t seem to be performance-related but something else, I got it on some 3D games made with Godot in the MechJam too. Not sure there is much to do on your side besides trying a different render pipeline, however having the option to toggle fullscreen with Alt+Enter really helped, so it’s good that you kept the native toggle fullscreen enabled in the Player settings (note that the window is not resizable and keeps around the same resolution, but fortunately it the maximized window was just enough to play and I didn’t have a big window cut-out on the edges preventing me from playing).
Sin & Punishment 1 is probably only available on Nintendo Online now (via N64 emulator), and Sin & Punishment 2 on the Wii and Wii U eShop (until March 2023).