I’ve been working on a house re-model design for many hours, saved for lunch, closed the file & returned to see an error message ‘Failed to open’ on my screen. No way of opening a file. Similar to this sketchup forum link; Student file-->FAILED TO OPEN DOCUMENT
There’s not much in that file and unfortunately enough of it is corrupted and can’t be recovered. Where have you been saving the file while working on it? Do you have a .skb backup copy of the file? If so, change the extension to .skp and try opening that.
Your profile shows you have a SketchUp Pro subscription. That includes unlimited storage on Trimble Connect. Were you using that to save a back up of the file?