I feel like this line of code is a bit noobish, but I didn't know how else to check PsetProperties, since there's no way to check all items of a dynamically generated enum in Blender:

if f"'{selected_pset}'" in str(prop.getPsetNames("", context)):

Almost there, I've made a few tweaks and merged :) Here's what you missed:

1. Property sets can be added to graphical objects, true, but they also be added to all sorts of other fun non-geometric things like materials, portions of materials, construction tasks, resources, schedules, and even standardised structural profiles. Isn't BIM complex and fun? :) So selected_objects only works for one type of pset assignment.
2. Any selected element that is not a BIM element should be skipped.
3. To answer your question, you can call blenderbim.bim.schema.ifc.psetqto.get_applicable_names directly :)

Really appreciate your contributions! Keep it up!

Awesome! :)