can't access due to UK online safety act
Well, technically, it's likely because he has decided to block UK IPs (or similar). A form of protest I assume, assuming he runs no business in the UK and no other reason to think the UK Gov has any interest in policing an .com blog run by someone who doesn't live there nor hosts the website there. (I'm not against that form of protest per se, but let's be clear about who's doing the blocking)
Or to avoid the fines and/or to avoid integrating some age verification service.
Maybe symbolic since it unlikely the site would be prosecuted, even if they were in violation in some minor form. It is easy to be in violation to my understanding since it does not need to what is posted by the site owner as part of the blog but could be in the comments.