Steam -might- also try to redownload & reinstall the game the next time you restart. I think I've seen something like this happen, but my memory is hazy on the matter.
It's advisable to uninstall Steam games from within Steam client, in any case.
You would have a lot of leftovers in files, registry and whole Steam library.
Besides, that would be much more work than properly uninstalling the game. Best to use an uninstaller program like Revo or IoBit uninstaller that would also clean up all residues that cane come back and haunt you afterwards.
That goes for all games and programs.
I'm genuinely curious - Does that still really matter, except for tidiness, for the typical video game, for any reasonably modern setup? I knew they somewhat did when the norm was 20-40GB of HDD and 128-256MB of SDR, or for productivity and utility programs that would otherwise have left a lot of dangling file associations and menu options.
Also having trouble seeing how the residues from a game uninstall could come back to haunt, except for maybe old settings, old profiles, and old saves, when and if said game is reinstalled someday.
I concede that they can and do add up eventually.
Most standard uninstallers these days would also do an acceptable job, in my experience - But I don't touch anything known to be dodgy or clingy.