Welcome to the forum.
Spellcheck is probably in the same situation I am - it thinks it's not a real word. I was very surprised to find (one) listing for it in Google, with "supposedly" given as a synonym. The example sentence given for it is "He is presumedly buried in Tanglewood Cemetery". I would word that as "He is presumed to be buried in ...".
Until today, I don't think I'd ever come across the word.