FTP decrease after 6 weeks of inactivity due to surgery - What to realistically expect?

The closest I’ve been to being off the bike is 5wks after surgery to remove a bowel (colon) cancer. I arbitrarily dropped my ftp by 50 w (290-240w IIRC) with the intent that if it never felt right and/or my HR wasn’t right I’d change it again. It felt right though.