I solved this by making a converter that intercepts what is coming from the TRV and altering it to the external_temperature that has been sent to the TRV. And so far, it works perfectly showing the correct external sensor room temperature in the original climate card without using custom cards, faux climate devices etc…
You can find it here, and it really only requires you to copy a file and changing one line in the z2m config file.
Since some years have past, I’ve created an updated blueprint for ZHA, using the external temperature field of the updated zha quirk and I improved the description based on your very helpful explanation with post #5
