Ornaments and grace notes need to be improved
I use ornaments and grace notes quite often, and what bothers me is that the playback isn't accurate. I know it shouldn't matter since I'm creating sheet music, not midi. Others have also suggested doing some work-arounds, like using invisible notes etc. I find doing all of these compromises for every ornament and grace note really grindy. The thing is that I compose for instruments I don't play, so the MuseScore playback is all I get when I'm composing. I don't know any classically trained musician who could come over and do a demo on some of my pieces (aside from a few pianists, which defeats the purpose because I play the piano myself). When I hear MuseScore play an inaccurate playback of a passage with ornaments or grace notes, it instills in my mind that that's how it's gonna sound when played by a person.
Here are some, if not all, of the problems with ornaments and grace notes in terms of playback.
-The length of an appoggiatura can't be adjusted.
-Appogiaturas that come after a note don't play at all.
-Trills and turns can't have accidentals added onto them.
-Trills and turns don't play on short notes (put a trill on a sixteenth note at 140 BPM; it won't play the trill)
-Turns can't be adjusted to play in the middle of the note (https://en.wikipedia.org/wiki/Ornament_(music)#Turn)
-Cadenzas are extremely difficult to notate (I can't image recreating this in MuseScore: https://upload.wikimedia.org/wikipedia/commons/1/1f/Chopin_nocturne_op2…)
-The dynamics on a sforzato can't be adjusted.
-Sforzandos (sf, sfz, etc.) act like dynamics, when instead they should act like sforzatos.
-There is a bug with tremolos where extremely fast tremolos (eg. a 32nd note tremolo on a quarter note at 140 BPM) don't play throughout the duration of the note, and there is a split second of silence before the next note plays.
I suggest that some feature could be added into the master palette or the inspector, where you could select certain options. For example, for trills and turns, there could be an option for adding an accidental on top or at the bottom. For appoggiaturas, there could be an option if the note should be the length of an quarter note, eighth note, etc. In fact, this feature has already been implemented into fermatas, where the duration of the pause can be adjusted.
I know it takes lots of time and effort to implement features like this, but this is something that really needs changing.
There is definitely room for improvement and some discussion about possible ways this could happen. However, there are actually already solutions for several things you mention: