For what it is worth, I have an older Mac and newer iPhone and newer iPad. Notes on the Mac is an older version of Notes compared to Notes on iPhone and iPad. It seems impossible to tell exactly what Notes version — not OS version - you have on each device BUT if one device is older, it stops some notes syncing across all devices. In my case if I create a note using Tags or tables on the iPad it does not sync -even between devices that could use Tags, because one device does not use Tags - in my case my old Mac. A message does pop up saying This note in not supported on some of your devices. It means not supported on ALL your devices and so won’t work on ANY device - that’s just ff’ing great, if you ask me. I’ll try to disconnect the Mac from all accounts used by Notes and only use Notes by logging into iCloud and see what that does. In the meantime, I’ll keep the notes in Notes very simple.
UPDATE using new features on new iPad, DOES sync on new iPhone. But not on older Mac - so I’ll browse to iCloud on the Mac to access Notes to see if the new features are syncing there.