Someone seem to have found a workaround and i quote "I had the same problem and was able to get around it by entering desktop mode. I created the new character there, then saved it and went back to gaming mode." also to quote the Developer from this forum

"I'm really sorry, we didn't develop Our Life for the Steamdeck and don't recommend people use it on that system currently. I think Steam declared it "playable", but we didn't ask for that. Some people have found work arounds for this, like by entering desktop mode when making the character, saving, and then going back to gaming mode. However, there's not a full fix for it right now."

I'm copying my reply from the other discussion, but yeah, I'm sorry. Steam gave it a "playable" status despite us not submitting it for the Steam Deck. That error didn't used to be a problem though. We do hope to fix it next year.