My understanding is that a handful of instances on the fediverse have geo-IP blocked the UK rather than open themselves to legal trouble.

I would guess that the others are either operated outside of anywhere that the UK can enforce its rules, not beholden to the new rules (I believe I read that there is a minimum user count for them to actually apply), or are just winging it.

I'd be shocked if more than maybe 4 instances of systems on the fediverse even had the resources to try to comply with this.