If I click on Workspace Options in Write Mode, leave the dropdown menu still showing and then open a different program, the dropdown menu is still visible above the program that’s just opened. This happens on both my Macs - iMac Pro and Macbook Air and in all Dorico Modes where Workspace Options is active.
I haven’t checked it fully, but it looks like the same behaviour occurs in the Mode Selector that appears when Dorico operates in a smaller window (e.g. half the screen on a 13" MacBook Air).
Same with the tempo slider, I found back in January.
Unfortunately there’s nothing we can do about this at the moment. There are good, but rather boring, technical reasons related to the fact that we are in the middle of a transition from one user interface framework to another, and while we’re in that transitional phase, some of these kinds of niceties (and also things like tooltips) are casualties. These kinds of rough edges will be smoothed off when we are able to complete the transition – which, to be clear, will not be during the Dorico 4.x lifecycle. We’ll be dealing with these kinds of issues for a little while yet. Hopefully they don’t unduly spoil your enjoyment of using the software (I, at least, am able to live with them).