Compare it to switching out the surface of the table you play boardgames on - different surfaces might feel differently, look differently, but ultimately all serve the same purpose and a game board will work the same on all of them. So really, it's mostly about finding a desktop that you like.

(We can go into details about differences, but for starters, this analogy serves well enough)

KDE is bot a way to play games, it's more of an entire desktop. If you miss having navigation bar at the bottom or a desktop full of shortcuts, try KDE.

Be a bit careful on what you read on the Internet regarding performance of either of the two. For some reason there is a lot of tribalism around people's favorite DEs which leads to a lot of misinformation.

Gaming Performance is almost the same, just pick what works best for you: https://www.phoronix.com/review/kde-gnome-wayland21/4

Across all the games tested both native and titles via Steam Play (Proton + DXVK), the GNOME Wayland session most often was showing the best performance and across the wide range of tests carried out came to about 4% better performance than the GNOME X.Org session. The KDE Plasma Wayland session tended to perform slightly in front of its X.Org session as well for these Linux gaming tests but there were a few games still running into problems with the KDE Wayland session.

Yes. KDE is in fact much lighter and faster than GNOME. Apart from lower RAM usage, it taxes your CPU and GPU less.