Gradience mainly changes the looks of libadwaita applications and it only work on gtk3 and gtk4 apps if you use the adw-gtk3 theme.
There is an important difference between gtk4 and libadwaita. While libadwaita apps use gtk4 in the background, they cannot be themed through normal gtk theming.
I don’t know of any way to change the compactness of gtk4 or libadwaita, sorry.
where to get games:
this will not probably work for most multiplayer games or always-online games like Genshin Impact
Lutris is a FOSS game launcher for GNU+Linux that handles installing from different (open-API) sources like GOG or itch.io or just a local installer file. It also manages wine/proton versions, settings and prefixes for each game. It also integrates with a lot of emulators for old consoles like 3DS, PSP or Atari.