Testing it now, doesn’t cost that much for a year! Gladly support.
I made sure to deselect syncing Filters and Notes/@Trash folders of NotePlan.
Wow, it actually works… Shows up on my PC and changes made on PC, shows up on Mac. Very quickly without any “reload” actions.
Tested iPhone app, changed made there shows up everywhere too!
Both Obsidian and NotePlan 3 has to be open for this to work. Only iPhone and Obsidian won’t work. But still! Will continue testing tomorrow.