“Can be avoided this “… can’t be found”?”
To answer your question in one line: YES
“Is this a normal behavior?”
That’s because there’s no template file setup to display at that segment of the URL structure.
By default, there’s no template for domain.com/category/ however, there is a template for domain.com/category/category-name/.
WordPress refers to: domain.com/category/category-name/ as a “taxonomy template”. But in my eyes, it should be labeled more so as a “term template”. Just for the simple fact that the contents on this page are likely revolving around a term object, within the category taxonomy.
WordPress refers to domain.com/category/ as a 404 not found, because there’s no template assigned to this url segment. In my opinion, THIS is what should be referred to as the “taxonomy template”.
I’ve asked a question and answered my own question on this very topic. I’ve also written a blog post (which goes into slightly more detail) to override this template structure and functionality if you’re interested. It allows you to create a specific template file for term.php and taxonomy.php so that you can have both a taxonomy archive template AND a term archive template.