I'm having the same issue, but it's ANY text box that submits data. I've followed the steps in your reply and it DOES clear them, and I can set it to clear them every time I close the browser, but I would like it to never record them and offer them as suggestions, ever; because as soon as I go back to the page and answer a few questions, it just stacks up with this really annoying popup that I can't seem to get to go away.
I even went to edge://flags/ and disabled "Show Autofill predictions" and it did not fix the problem after restarting edge.
Windows 10 Version 20H2 (OS Build 19042.1165)
Edge Version 92.0.902.84 (Official build) (64-bit)
I've been looking for a solution for about 45 minutes and I'm starting to think that it's to just go back to Chrome.