I have a clue what the poster is on about. It has happened to me:

Start Valheim. Press F2. A chat window opens in the upper left portion of the screen.

That is what chrsyt is complaining about. I do not know whether Valheim is the culprit or Steam. I do not know how to re-map that key via Valheim or Steam. I do know that I eventually stopped fat-fingering the keyboard during combat.