Alright, this was fixed via Settings / Reading / Static page / Posts page: Blog.
Thank you.
Only one visual thing remains – can the “Blog” category (or Posts page in general) name somehow be displayed/propagated as the headline at the top of the “overview” of all blog posts, just like there is a name of a page (which is listed in the top menu) written at the top of each page?
When I click on Blog, now I have:
Entry 1
Entry 2 etc.
What I would like to have is:
BLOG
Entry 1
Entry 2 etc.
with the headline in the same style as headlines on pages.
Is that possible in an easy way? Thank you.