imdb.com seems to have forgotten my email, and it won't let me create another account.

A link to the Help page is at the top of nearly every IMDb page.
But you found your way here, so you probably know that.

Found in the fine print at the bottom of the Help mainpage:
https://help.imdb.com/imdb

• Issues logging in to IMDb? Get login help.

Which should lead eventually to:
https://help.imdb.com/contact
I'd use the button for Log In questions.

I wish you smoother sailing from here.

well, that contact page leads to the login page, that says "Log in for IMDb general Support". but I can't log in, that's the problem.
I did send an email, although I could only choose "sign-up issues" as category, beacuse there's no log-in-issues choice.

But if you just close that pop-up, you can fill in the contact form choices (you may want to choose others):

And then fill in this form:


I know it says again for you to login, but are you telling me you cannot submit this form without logging in? The message at top does say "full contact options", implying you can use limited contact options without logging in. And you are providing an email address within the form, so I would assume you can get help with logging in using the form that claims to be for that purpose.

If not, then that's a second issue that needs to be addressed (your login problems being the first.)