You should be able to check your Steam Cloud data by logging in here:
https://store.steampowered.com/account/remotestorage

Since the Valheim safe system overhaul, you should also be able to move your save files for worlds and characters between Cloud and Local. If you don't trust the Steam Cloud, you can even turn it off for Valheim entirely (AFTER you've moved your files to local).
You can always make manual backups of your save files.

If you want to know more about the old and new save system, you can check out the pinned threads in General Discussions and the Bugs & Technical sub-forum.