Upright bass slapping

I guess you mean you want to 1) notate playing the bass 'normally', AND 2) notate the slapping as seen in the video. I don't know if a bass TAB offers this facility - somebody may jump in and help this discussion.

As for the authentic sounds of slapping the body of the bass, I don't think there's any sound in the standard MuseScore instruments pool (in the program, by default). But you might consider something like the conga, which has (at least) 3 possible different hitting-the-conga-drum-head sounds. If you added a single-line percussion stave, chose 'conga' for it, and RENAMED the score name as something like "body slap", at least you could include that with the bass-playing notation AND sound.

I resorted to using 'conga' for the inclusion of a cajon in one of my compositions. Inside MuseScore, the cajon only has one sound. But the cajon can have (at least) three slapping/percussive sounds (that I wanted). Not a perfect solution, but illustrative enough.

The score where I did this: https://musescore.com/user/35459860/scores/8420936