Apparently, if you add the mods Better Third Person View for 1.18 and choose a inchling, you can x-ray.

I also have Nimble added into my modpack, so it might be a mixture of both perspective mods.

Inchling's size change relies on Pehkui, I suggest reporting it there instead; I can't do much without invading on base Pehkui stuff

Appears to be fixed in the latest version of Nimble.