Got it finally 😄💪
Customer Service proposed me again to install the latest version (8.35)
But also V8.35 didn't bring me any further.
I remembered though to have read somewhere that codecs are being installed by the app on demand ...
So I decided to start VideoPad once as administrator (Run as Administrator) and now it just runs as it should with sound.
So every time a want to include a new format, I need to start once as Admin, and from then on, I get sound for that codec.