I'm not familiar with all frameworks you listed, but i've worked extensively with spring boot and i can assert you that it's not a opinionated framework (as in one way how to do things correctly). Blazor and Phoenix are niche frameworks that don't have wide adoption outside this site. Django has a shared history/competition with Rails but it's also not widely popular.
> We take an opinionated view of the Spring platform and third-party libraries so you can get started with minimum fuss
Spring Boot is definitely opinionated (this is taken from their home page). Maybe not as much as RoR, but saying it isn't at all sounds very strange to me, having worked with it for a few years too...
> Django has a shared history/competition with Rails but it's also not widely popular.
Are you sure? Django is insanely popular. I am not sure on what basis you are saying Django isn't popular. I posit Django is more popular than Ruby on Rails.
Django is super popular.