Musescore Preferences - Note Input - Play Notes When Editing
In the Musescore Preferences -
Note Input -
underneath "Play Notes When Editing", you can adjust the default duration.
It would be cool, if there was another box to adjust the default velocity, which is fixed at 80 at the moment.
Just turning down the volume is not ideal for me. As the piano-sound changes with the velocity you could then adjust the default piano-sound for entering notes as well.