I thought about mentioning that but removed it since the invites would really only be able to come from the admin and maybe a small select group of people. Setting up an invite system with a spreadsheet and involving more than just a few people would likely become a messy and complex endeavor very quickly.
I don’t think Lemmy has it (there is an open issue for invitation links that I don’t believe anyone has worked on). I don’t think MBin or Piefed have it either. Not sure about Mastodon. The beauty of FOSS though is if someone wants it bad enough, they can implement it themselves.
If that’s something you want to try out, then set up an instance and try it out.
This is pretty normal. Every time there’s a big wave of new fediverse users, a big chunk eventually goes back to their original social media. Some portion will stick around to be regular users and the cycle will repeat again next time a social media company pisses off a bunch of people.