1. Shift M to select all muted regions.
2. Run Key Command "Deselect All Regions except on selected Track." This is an unassigned key command, so you'll have to Learn it to a keystroke.
In tandem, these will leave selected only the muted regions of the selected track.
6-core Mac Mini 2018 with 64 GB and OS 11.3 running Logic 10.6.2, 8-core Mac Pro 2.8 (early 2008) with 16 GB RAM and OS 10.14.1 running Logic 10.4.3, Mac Mini Server mid-2011, Logic Control, Vienna Ensemble Pro (VI and Synchron), Vienna MIR, Ivory