[dysoco]

I remember John Carlos Baez having some interesting stuff: https://johncarlosbaez.wordpress.com/

Some other ones I had bookmarked the other day but haven't seen much in depth, mostly computer science based but more towards theory/math side:

https://blog.computationalcomplexity.org/

https://semantic-domain.blogspot.com/

https://greydanus.github.io/

Also go to Terry Tao's blog and look at the sidebar, there are a lot of links to external blogs there.