How to contact an add-on developer who has no contact info
I installed the Mail Link Enhancer add-on. It works, sort-of. The subject line and other fields included after the ? in the mailto address do not get filled in. Looking at the add-on info, the developer is Nick, but there is no contact info in the More Information section of the add-on profile. The add-on hasn't been updated since 2020, so I'm fairly certain that things changed since then and that's why it isn't working, but I'm no expert.
I can't see that add-on, but you can go to addon's page, select some stars in the Rate your experience section and write a review. It should be send directly to his e-mail.