It would be very convenient at times (in pose mode) to
Obviously since "Copy Transforms" only exists as a constraint, there is no such operation as "Apply". I think I can create an add-on as an exercise, although this has probably already been done. (I'm thinking only of disconnected non-parented control bones.)
Mesh/empty to mesh/empty might also be useful.
Or perhaps I am missing something?
since "Copy Transforms" only exists as a constraint, there is no such operation as "Apply"
Yes there is: CTRL+A when hovering over the Constraint, or clicking the "down arrow" next to the eye icon for the dropdown menu...
Or do I not understand what you mean, maybe?
I'm afraid I don't see a down arrow on Constraint (where there is one on Modifier):
Oh sorry, I didn"t know that was a new feature:
It is also in 3.0 Beta, but as you noticed not yet in 2.93.
Blender 3.0 should be released in about two weeks and the Beta is already very stable, so...