Tremolos, Trills, Glissandos, Crescendo and diminuendos

The problem with having MuseScore play them is that how they are played is really up to the artist's interpretation. The MuseScore developers don't want to limit the users in that way, so they have simply opted not to have the software define these things.

However, there are ways around this. For the tremolos, trills, and Glissandos, you could write them out properly with the notation MuseScore gives you, and then in the Second voice, write what you want to hear. Then you set the second voice to invisible (so when you print it out it doesn't come out all wrong) and then you set voice one to have zero velocity so it doesn't interfere with voice two.

As for crescendo and decresendo (diminuendos), you could put in the crescendo/decresendo and then fill in the ends and middle of it with what's available from the dynamics pallate to create a more gradual increase/decrease in volume. Then of course, you could also set those dynamics markings to invisible if you wanted. It's not perfect, but it works for listening purposes. I suppose if you wanted to get really extreme with it, you could individually set each note's velocity to suit your needs, but that might take longer than it's really worth.

There are similar processes for things such as ritardando, other types of tempo changes and other things that you wouldn't necessarily want the software to have control of.