I often have to install taps that have that same setup (wall plate and tap that screws into it), and have the same problem but it’s much less of an issue as a temporary water supply on a building site.
My guesses would be using a nut as a lock ring like you suggest, or to get an oring/gasket that sits inside for it to tighten up against.
So far I'm seeing loads of PTFE being used but I can't see it lasting. I'll try a plastic washer as well or as you say, an o ring. The fit needs to be tight though to stop it being turned the other way.
PTFE tape is fine once it tight enough if you use enough and you get it into position it'll be fine. Who's actually turning taps once in place apart from to turn them on.
I often have to install taps that have that same setup (wall plate and tap that screws into it), and have the same problem but it’s much less of an issue as a temporary water supply on a building site.
My guesses would be using a nut as a lock ring like you suggest, or to get an oring/gasket that sits inside for it to tighten up against.