Can no longer mark up text just by typing?

I am an editor who occasionally works on PDFs via the Comment function. It used to be that I could just start typing to insert text at the cursor, or select text and start typing to replace it, or backspace to delete text, and so on. Today, all of a sudden, I cannot do this—I have to go up to the toolbar and click on the buttons. Suffice it to say, this is majorly slowing me down. I am on macOS 11.6; Acrobat Reader says it is up to date (v 2021.007.20096). Is there some way to restore this functionality?