Forgot password and email suffix... am I bucked?

When you say Bing, I assume you actually mean the Microsoft Edge Browser, and its password manager.

When it comes to recovery, having access to your email is the best thing you have. If you're trying to figure out which username+suffix you used for a particular login, assuming you keep all of your emails, this should be possible to determine by opening up an email from the website, and looking at the To: line. This should include the full email address that they sent the email to, including the suffix. Searching for a service may help you find those. Test searches for to:username+*@gmail.com (a wildcard) didn't work for me in my tests. However to:username+suffix@gmail.com produced results that were only to that combination.

Your best bet here probably, is if you're looking for, for instance, an Amazon account, search for from:amazon.com which should get you emails sent from an amazon.com domain, and look through at the email header for the "To:" line again. Repeat with the email addresses you have access to.

Also, please, please, get yourself on a proper password manager. These are designed, and purpose driven to hold secrets in an encrypted manner, and be usable from your desktop browser, a phone, another computer, etc. Bitwarden is a popular choice, and what I use. Start cataloging your accounts there. If you're reusing passwords, stop that, and aim for more secure generated ones in the password manager you choose. I don't know 99% of the passwords in my vault. But I do know my vault's password.

If you are having trouble finding some accounts, contacting support at a certain website may be required. Many understand the +suffix trick, and count those as the same email address as your plain @gmail.com address when doing account recovery. Just know that you may be asked for details so they can be sure you're the person that controls that account.

I hope this helps a bit! Good luck!

Search for email from whatever the service is, the plus address will be included in the To: field. Then it's just normal forgot password recovery flow.

E.G. If it was service was Ebay, search for ebay in your inbox and then go find an old email, open it, and expand the header to show the To, From, Reply-To, Date fields in order to find the plus address in the To field.