Hexbear started during the 2020 BLM protests, where cops were using social media and internet presence to track down activists. They are still doing this, but with less vigor than when police stations were burning down.
This included things like using tattoos on naked bodies, etsy store receipts etc.
Just before the r/cth ban, there was also a problem with chasers and leering objectification, and steps were taken to reduce thirst-posting and the like.
These things combined means that people don't post selfies or direct identifying information. People post their pets and artwork, but I know I have to make a decision about where and when I post things to make things non-trivial for cops or random chuds. I feel like a unique pet name, breed, and rough region could be enough to track someone down.
Even so, I think I'm bad at it. I feel like if someone knew me and read everything on hexbear they could ID me pretty easily (and I know multiple people in person on hexbear, but we've never exchanged usernames).
Idk if there are any hard and fast rules beyond the selfies and direct ID though. I should burn this account.
Edit: removed reference to masculinity
If you mean the Firefox Multi-Account Containers extension, then that's fine (although I have issues with cookie management in that), but just switching a user-agent is not enough to stop fingerprinting and cookies. Some new features like cookie bounce protection in the latest update and the enhanced tracking protection can kind of prevent this leakage, but remember that it's a numbers game and you need to be lucky always to not give anything away that could link your account to an off-site account.