@wojtek Could you provide me with sounds/tones for use in those cases?

Maybe this pair: https://freesound.org/people/rhodesmas/sounds/322897/ or this https://freesound.org/people/rhodesmas/sounds/322930/ https://freesound.org/people/rhodesmas/sounds/322895/

licence-wise they should be ok (CC3.0)

I'm not convinced with those sounds and their licensing. I know that with CC license we could use them and "mention" authors on the About page, but the question is: "Would that be OK?". If we would use more sounds (from many authors) it would be impossible to "know" who authored what, etc.

That's why I've decided to try to use a different route. I've recalled that macOS has some sounds embedded and tried to use them. Those sounds will be used in the next build. Please let me know if they are "OK" - for me they are better as those sounds sound more "native" (user knows them).

Good idea. They sound ok (could have probably went that way in the first place…)