Best I can figure is you are reporting that:
You can not select a midi track from a midi style to be inserted into a RT style when the midi track you want is on a Utility track of a midi style. Instead you can only select midi from a legacy track of the midi style.

No surprize to me. Historically, midi files only generated midi on legacy tracks. In fact, I suspect that is true today. So this restricted menu option is by design.

But, I am struggling to comprehend all this code as much or likely more than most of us! crazy

BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, 1TB WD Black NVMe SSD, 2TB WDC Blue SSD, 1TB WD Blue, 2 TB SK NVMe, 6 TB External, Motu Audio Express 6x6