I currently move my mail system away from W10 to an isolated Lubuntu VM (in Virtualbox). I did his for safe browsing and other purposes (Sec tests with Kali etc) already. The goal is to move away as much as possible from W10, replace it as the Virtualbox VM host by Ubuntu+Cinnamon.

I customized KMail (within Kontact) and can send ? receive mails. Outlook pst migration will be done via Thunderbird import -> EML Export.
However, in Kontact, the component sidebar is always strethed (approx. 4 times from what I usally see in screenshots).

I can hide the whole sidebar, but then would need to toggle it for another module.
--> what's wrong there?