> A buggy app accumulates gigabytes (literaly, i am not exagregating) of temp files there, but i cant visit the folder to delete them.

Settings > Apps > select the app > Storage and cache > Clear storage.

No, I dont want to clear storage - there is data I downloaded into the app and work with that I dont want to lose. But the app also accumulates some temp files there.

without access - how do you know the files are temp files?

I used to delete them on old Android version.