For those that haven't read the bug reports above, it's now a confirmed bug with Chrome 85, so you will need to wait for google to apply a hotfix (hopefully in the next week or two).
Also to clarify, it not only affects this forum, but just about every website that uses any of the 4 most popular third party rich text editors, so it a very widespread issue.
As a temporary work around you can click the cog / gear icon on the editor toolbar to switch to basic text editing and turn off rich text. Or you could use another browser on your device.