Category permissions in Discourse are based on group memberships. So for a category to be accessible only for users with at least 10 posts, you would need a group to which users are added automatically after 10 posts.
If you only want to avoid scammers, I think you could switch to using the trust level system of Discourse and allow only users with trust level 1 or 2 and up to access that category.
But trust levels are more based on reading and spending time interacting with different topics in the community than about posting.
Without a plugin, you cannot add requirements. You can only adjust the ones that Discourse provides. Trust level one is only based on reading.
| activity | default | setting |
|---|---|---|
| Read posts | 30 | tl1 requires read posts |
| Visit topics | 5 | tl1 requires topics entered |
| Total reading time | 10 | tl1 requires time spent mins |
Trust level 2 requirements offer more criteria. You can include things like days visited, likes received, and replies to topics created by others. So it could be configured quite close to your current 10 posts.
| activity | default | setting |
|---|---|---|
| Read posts | 100 | tl2 requires read posts |
| Visit topics | 20 | tl2 requires topics entered |
| total reading time | 60 | tl2 requires time spent mins |
| Days visited | 15 | tl2 requires days visited |
| Likes received | 1 | tl2 requires likes received |
| Likes given | 1 | tl2 requires likes given |
| Reply to topic | 3 | tl2 requires topic reply count |
If you don’t want to use the built-in trust level system, take a look at Discourse Dynamic Groups, which allows adding users to other groups automatically based on some criteria. Or you create a custom badge and use the User Group Membership Management Through Badges automation
Currently not, but I am interested to find out. Are you admin or moderator? Is there anything special about the group or category? If you look at the “Allgemeines” section without changing anything, is the save button disabled there too?