Steinbock: "In my case switching the Permalink (/wp-admin/options-permalink.php) from Post to Plain and back solved the issue!"

Thank you so much, Steinbock! I had been struggling with this issue for days and tried countless solutions, but this was the only fix that actually worked. Switching the permalink structure from 'Post' to 'Plain' and back again solved it instantly.

I even created an account just to upvote and thank you, but I didn’t knew I needed reputation first—so here’s my appreciation in a comment instead!