Is it possible a film studio, or legal agency, could set up a Lemmy Instance and then capture all our IPs?

Absolutely. One of the biggest child porn groups is an FBI front for this purpose. I’d google the subject for a link but umm…no

So basically the only thing protecting our anonymity is the relative unpopularity of Lemmy?

To expand on this. If you are talking about anything online it is not private. That doesn’t matter if it’s in a WhatsApp chat, a telegram chat, a Lemmy post, a Facebook feed, etc. as soon as it hits a computer if someone wants to see it they will. There’s just hurdles to get it.

If you want anonymity stop using computers.

Tell me you know nothing about computers without telling me you know nothing about computers.

CC BY-NC-SA 4.0

Says the guy licensing his own comments on social media.

Tell me you know nothing about copyright without telling me you know nothing about copyright.