Editing text in documents in personal vault

I have a sensitive document in my personal vault. I also have Microsoft 365. I can't seem to be able to edit the document in the vault using my android tablet. I  can do it on my pc, but I'm not always near, and my memory isn't good enough to remember what the changes were by the time I get to the pc.

Curiously, the page opens in black and white, but rapidly changes to sepia. Very odd.