Is it possible te create a category where users can see own topics only?
(I need it to create a “support” category, but I don´t want users to see other users questions)
You can’t have topic-specific permissions in a regular category, no.
The best way to do this is using a ‘group inbox’. There are a few descriptions of how this works - here’s one comparison of categories and group inboxes:
We describe how ‘team Discourse’ use group inboxes in this blog post: