I’m really grateful for this article from a few years ago by Marco Venturi:
It was about exactly what I wanted to do (load WP content within a static html page), but I couldn’t get it working with the original code – I’m not a js savant – but updating to the current version of Bootstrap (5.3.8) did the trick! I had to spend some time comparing current .modal code from the BS docs – mainly updating data-target & data-toggle calls to the current data-bs-target & data-bs-toggle.
I just wanted to share the fix and again to thank Marco Venturi for his helpful contribution.