Non-paywalled link: https://archive.ph/noqtk

found it! https://yourdigitalrights.org/ :)

https://justdeleteme.xyz/ and https://simpleoptout.com/, there was this one website that had a pre-filled email template too, and it’d remind you to follow up with support, etc. Even while this isn’t for data brokers, it’s good to have these just in general.

I highly suggest Tuta, https://tuta.com/, or other conventional mail boxes like https://mailbox.org/en/