HDR10(+) content is not tunneled, so you will see 12-bit YCbCr as you already mentioned.
Switching to FEL will improve image quality usually (often with regards to brightness), but it does vary depending on the movie. And yes, using TV-led output with FEL will still use RGB tunneling.
If you’re using a projector, you might want to take a look at a special build of CE21-NG, made by @cpm that has more options to tweak the output with regards to peak brightness levels etc.:
Releases can be found here: