Retropie UI resolution vs game emulator resolution....

Hi all! Retrobat noob here, migrating over from Retropie land. I have a question about the emulation performance based off the resolution of the windows desktop. For starters, I have this mini-pc that I'm running Retrobat on:
https://www.bee-link.com/catalog/product/index?id=455

The cliff notes version of the specs are:
Beelink EQ12
Intel Processor N100
16 GB DDR5 4800MHz
M.2 PCIe x1 SSD 500gb
running to a single monitor at 4k

As i've been reading to prep before I start copying roms over, I read in a few place some systems (like n64 emulation) struggle running at 4k. My questions are:
1.) does the resolution of my Windows desktop affect the resolution the game runs at?
2.) If it is an issue, is it possible to have my Win Desktop at 4k, but force the games to run at 1080 for better performance?

Hello and welcome

In any case, you can choose your resolution within the Retrobat menu. So you can tweak, adapt from there the setting to adapt them for each system, even for each game.