Scrapers are getting so bad that the lemmy containers are falling over, so I’ve disabled anonymous access to allow legit users to continue using the service. I will work on improving filtering so I can reenable anonymous access. Apologies for the inconvenience.

Go to the site configuration page in the admin section, then look for the checkbox labelled “private instance”.
Interesting. I’ve seen that option but this GitHub post made me think it would do more than what I wanted. https://github.com/LemmyNet/lemmy/issues/3148
I think the original implementation of that setting disabled public access AND disabled federation, however it appears the ability to disable federation was subsequently split into a different setting. (I have private mode turned on and we are still communicating across instances, so I know federation is still working). I am not sure that is what you were referring to, though…