Seems like admins can hide communities from all, local, and trending, unless subscribed

https://github.com/LemmyNet/lemmy/issues/2943#issuecomment-1581485335

https://github.com/LemmyNet/lemmy/pull/2055

curl -X PUT http://localhost:1236/api/v3/community/hide \   
-H "Content-Type: application/json" \
-d \
'{"community_id":3,"hidden":true,"reason":"controversal","auth":"Foo"}'

I haven't tried this, but maybe someone will find it useful and test it out. You could probably also easily do it in the database instead of using the API call.