I'm having the same issue. Way back when wheels were square, my Apple ID was associated with my old gmail email account. Since I became aware of how much of my personal information google was stealing from me, I switched to an iCloud email account and associated my Apple ID with that. The Feedback assistant seems to remember my old gmail ID even though I haven't used it for years and when I change it to the iCloud account it says "Unable to sign in to Feedback Assistant. Please try again later". I can't use my gmail ID with my iCloud password as they weren't the same thing and I don't remember what my old GMAIL password for my Apple ID was. When I go to the feedback assistant website (https://feedbackassistant.apple.com/welcome), it shows that I am not registered for any betas and redirects me to the main beta registration website (https://beta.apple.com/sp/betaprogram/welcome) even though I must already registered as I got the Monterey beta) and when I click on "sign in" or "sign up", it just bounces me back to the same beta registration page and doesn't allow me to select a particular beta program (MacOS, iOS, etc) although it shows me as signed in. It seems that Feedback Assistant and the Appleseed program is using an old copy of the Apple ID database which to me is a huge security exposure.

Me too. It appears that they are changing the way the Touch Bar works as I get a zoomed view of it on the bottom of my screen but none of the keys (including esc) work properly. I'd enter this through Feedback Assistant but there is a bug in that as well!

These were all useless answers... especially the one from PBK saying that the message tells you all you need to know. It VERY obviously doesn't if this question has been viewed 26,000 times! The solution is quite simple actually. Go into your iPhone (or other device) settings. Scroll down to Privacy and Security and enable Developer Mode. Reboot, follow the prompts to enable it (you may have to reboot your iPhone and your Mac once more if the versions are out of sync) and Bob's your uncle.