If I had to do this I would go through my inbox and look for the "verify your email address" emails and compile a list of website and logins to delete. If you don't use a password manager, I don't see other solutions

There's no way to search to find all of them. Perhaps you could look through leaked password databases like Have I Been Pwned. And as @riccardo said, you can look through your email and password manager.

Once you get done with password managers and email, you can try using this list of most popular websites to job your memory

https://asciinema.org/a/9dwog4uqepaghpvyeginwckpn

if you follow the instructions, you can run a comand like

grep '.com$' top-1m.csv | head -n 200

and see a list like this:

https://paste.gg/p/anonymous/b95ebd306aeb4144a3456475c5328dfc

You could try waiting for a new change in laws concerning privacy, such as the GDPR and wait for the flood of incoming emails about companies which changed their privacy policy.

Do you use a password manager? If so, you could search for your email.