That depends on the game settings in steam. Valheim in library -> Properties -> General
In any case I would recommend to make a backup of the local map and character files

Saves are separate from your game files (like 99.99% of games) so uninstalling the game is not removing your saves.

I personally uninstalled / reinstalled teh game after the pydate and even removing the game folder (since I had a few old mods lying around) and I did not loose any of my saves.