Go here - Your email should be listed under your display name. You do not need access to the email address to be able to log in you just have to know it. Display Name log in has been disabled.
If you have any issues logging in after the upgrade - I will be available via our Contact Us to help you. I know that it's annoying, but you can also use your google, microsoft logins and be unaffected.
I do not care if you use a burner email the point of this isn't to force you to put valid email addresses in, the point of this is to obscure your login information from your display name which is a security risk that has been patched in this version of the software.
You will not be logged out in the transition, you will remain logged in - so this will only impact people who log out every time when they leave the site or browse incognito.