Can't join two Archimesh objects (modifiers have been applied)

Hi everyone.

I’m trying to join my walls, floor, door etc, but after shift selecting multiple, Control J isn’t working.

I’ve applied all modifiers, and tried only combining 2 at a time as a test. No luck.

Any suggestions?

See in my image the room (walls) and baseboard are both selected, but I can’t control J

OK I’m a dummy.
Opened up a new file with just a square and a sphere and still couldn’t get it to work.

The catch? If you’re shift selecting in the hierarchy window on the right (not in the 3d view), you have to click on the 3D viewport one time to make Control+J work (I guess it’s a focus thing?)

*also note the viewport click has to be off of an object, just in the open space.

Hope it helps someone else.