People ask for help in chats or on Reddit or go straight to Bugzilla which makes it more likely the same question is asked a lot of times.
A Help category could keep support requests in one place. Discourse can offer similar topics to check out before posting to avoid duplicates (is that set up?).
Troubleshooting - After a solution is found, the most common problems could be moved into a single thread with one answer outlying the chain of steps to try when having this problem yourself - maybe replacing Troubleshooting - KDE UserBase Wiki ?
FAQ - We could also create/move here the most common questions+answers (How to solve problem X in KDE Plasma?) so people will find Discuss sooner in search engines.
I feel that will separate out the debugging process from the solution. Often, while the exact solution doesn’t fit a user, the discussion on the issue thread helps them fix their issue. So I’d suggest having everything on Discourse itself and not separating out to separate page.
If adding the auto lock thing, make sure that it doesn’t lock unsolved threads, or give a reasonably high timeout for unsolved thread to avoid necro bumping. Solved thread can be closed in 2-5 days of inactivity.
If you look at things like Stack Overflow’s success, it would seem that people don’t mind whether that solutions are in forum-like discussions, so my guess is that going to the trouble of transferring them to a wiki may be a low priority task.