Do nostr clients leak metadata when following content, or do they have al info on device and listen for relevant notes coming from relays?
Discussion
I'm not clear on all of your questions.
However I can see loads of clients visiting my webserver just for the NIP05 verification.
Say for example that I decide to follow #nostr within my nostr client. Would any information about me following this topic be visible for the network?
Every relay you use would get your client user-agent and IP address at a minimum.
The relay logs would likely also show the hashtag search request.
There's also a webserver which would have another set of logs.