Seems like they're creating a new account per post now.

Suggestions (keep in mind I don't know the technical viability of these):

1. Rate limit signups in Lemmy to one per 24 hours per IP (if I understand the rate limits correctly). Anyone requesting multiple accounts per day is immediately sus anyway.
2. Block their IP address
3. Use registrations the way they're meant to be used instead of rubber-stamping them with a bot
4. In addition to the above, check against a list of their known accounts. There's not an easy regex way I can see, but the account names all have a similar "feel" to them.

When I modded reddit subs I always had a karma minimum to post, it seemed to drastically reduce bullshit posts. It wasn’t even very high, like 100.

Preventing new accounts from participating will only result in them aging accounts for a bit before usage and discouraging legitimate new users from participating.

Exactly.