The OLSA is far from perfect, particularly in the definitions it uses, but its focus is social media platforms and the like, not simple blogs.

OFCOM has a q&a-based tool [1] to advise on whether the OLSA applies to a site. I'm not a lawyer, but its pretty clear that a non-adult-themed personal blog where people can post only textual comments on content that they dont control, is not going to be subject to the act.

[1] https://www.ofcom.org.uk/online-safety/illegal-and-harmful-c...