Insightful Agile Blog Sites

In no particular order:

Mountain Goat Software (Mike Cohn)

https://www.mountaingoatsoftware.com/blog

Martin Fowler (it's not really a blog site per se but there's lots of great articles)

MartinFowler.com

Agile Matters (Scrum Alliance)

https://www.scrumalliance.org/agilematters/home

Scrum.org

https://www.scrum.org/resources/blog

Adventures with Agile

https://www.adventureswithagile.com/blog/

Agile Alliance

https://www.agilealliance.org/community/blog

Superheroes Academy

https://www.superheroes.academy/blog

Agile For All

https://agileforall.com/agile-blog/