[2022] Accidentally loaded old cloud save (Ironman)

On the desktop PC go to Documents/Paradox Interactive/CK3/, in ther eis last_save.ck3 . That may be a copy of that campaign, depending on your recent activity there. To change copy it to the /save games/ folder there.

Whether that preserves the Ironman status I'm not sure though.

FYI there is no copy kept by Steam of overwritten saves in their cloud, so far as I know.