My dashboard is not opening with all the items displaying

The tiny icons are suggesting that MuseScore is having trouble detecting your display resolution. Anything unusual about the monitor or how it is connected?

I can't tell is the missing palettes are connected to that or if you just closed them, see if View / Palettes brings it back, and if they are tiny also or normal.

But also, try Help / Revert to Factory Settings, and if that doesn't fix the icon sizes, try starting from the command line (see the Handbook for more information) using the "-D xxx" option, where "xxx" is the monitor resolution in DPI. Or, since this is apparently macOS, see if there is some sort of setting that controls the scaling of applications for "retina" displays, and whichever way it is set, try the other.