When you run into a save error, please press F12 to open the console and send me a screenshot of the error log.
I'm hoping this is what you're looking for, this is for the manual save fail
and this one below is the autosave failure
I'm not sure if there's too much of a difference but I'll send both anyways, also let me know if any of that somehow leaks any personal info or whatever I'm definitely overthinking but just want to make sure