Hello,
I noticed that some of the forum categories are IMHO too nested, which makes it quite unconformable to post/look for topics.

Example:
System & Utilities - Dolphin:
- Dolphin General Discussion: General Dolphin topics can be discussed here. Please respect the Code of Conduct.
- Dolphin Help: You can report support requests here. If you have found a bug and you can provide step-by-step instructions which can be used to reproduce it, it should be reported at bugs.kde.org instead.

The description on both subforums is very vague and they could actually be the same.

Another Example is the digiKam, there are also subforums (which are hardly used), but you can also post just in digiKam (not in any subforum), which isn't possible in the dolphin forum for instance.

This is all very confusing and not really streamlined.

I would suggest to use only two levels at max (e.g. System & Utilities - Dolphin) and no further levels. Of course there can be exceptions in case of localized forums for instance or Amarok, but two levels should IMHO be the rule of thumb and not the other way around.

If there is interest I could make a list.

The nesting of subforums depends on the application maintainers. Usually we get asked or ask application teams if they want a forum, and if so, what structure they prefer.
Sometimes it even consisted of a complete own forum, which got imported into this one (see e.g. amarok, which was a forum long before this one). And sometimes the teams are quite happy with a flat structure, like k3b.

But agreed, a bit more structure and common pattern might be good.

Well, a good start would be to flaten the dolphin forum IMHO.

If you give me the rights I would volunteer.