I don't see this functionality in Lemmy. Mastodon has settings where you can limit your posting visibility to only those who follow you. But anybody that you don't expressly block will still be able to see your profile. More privacy features mighr be in development.

Probably your best bet is to keep your fediverse handle as anonymous as is possible. That would be the best advice I have to give. Also, don't give clues as to your whereabouts in your posts. Nothing on the Internet is trult private and infosec is hard. Always assume that a fediverse instance could be compromised at any time. Use some common sense and basic operational security and you should be okay.