Thanks! Some detail work has to be done, but the main issue is that up to "Reaper-534" my mixer looks fine like this:
https://photos.app.goo.gl/XWTNK1WnttKbghau8
But in newer Reaper versions one pan knob is missing:
https://photos.app.goo.gl/8SHTL9RpnnrE8gyL8
And the second thing that I think should be fixed is:
the clickable area around the folder button (not the button itself) is too small. If you want to hide or show children-tracks you have to click way too often until you accidentally hit the right pixel.
https://photos.app.goo.gl/6b2S9uiwuXZ366UPA
Maybe someone could fix that for me or could tell me how it's done?