If you have enough power on hand you can render games at up to 8K [0], and downsample to your monitor's resolution if you're exceeding it. The textures are the original 1080p assets, but it's still a huge boost in visual fidelity, especially if you're downsampling (there are also usually mods to disable a game's native antialiasing if you're doing this). If a game wasn't even attempting 60fps on the Switch in the first place, there are usually mods to unlock the framerate.

[0] https://blog.ryujinx.org/introducing-resolution-scaling/

Most console games end up having textures high res enough to look better than the original hardware if you render them at a higher internal resolution. There are some Wii and Wii U games that look spectacular if rendered at higher res, and the same applies to Switch.

If you emulate on fast enough hardware, for games that emulate well you will hit whatever the game's framerate cap is (sometimes 30, sometimes 60) flawlessly where the native hardware struggles.

Civ4 doesn't have 1080p assets but that doesn't stop me from rendering it in that resolution. I don't understand the argument. Without "good enough" textures I should render it lower and upscale after the fact?