And I lose everything I did from the last save point, I was just busy building a large storage building and laid out roads to it, basically built half a building and now I lost all of that, everything I did, might make me just not play on solo world anymore, so ♥♥♥♥♥♥♥ annoying!

Try verifying files if you haven't already, just to make sure nothing has corrupted since install.

I have verified files before, it started happening to me a few days before that last update a day or 2 ago.

Turn Steam Cloud off, only good advice I can give you. Before you do that, make sure to move your characters and worlds to local. There's a button in the main menu.

Valheim and Steam Cloud are pretty much never going to be friends.

Now that I think of it. Only been happening since the whole cloud save thing. That might be it!

It always was. ;) Some people had issues the way it was before, then people had massive issues with the prior patch, and now it seems other people have issues (again) with the latest patch.

Valheim dumps the entire world file instead of using a database like Conan: Exiles where only minimal changes need to be saved.

That's most likely what causes Steam Cloud to choke and throw up, taking everything else with it.

Turn it off, and your life will be much easier. Not only in Valheim.