Rey and Kylo are seen (almost) touching hands via Force projection earlier in the movie, so obviously physical things can be transmitted via it too.
I actually didn’t think they could really touch when I saw that scene. It’s possible, but they were in each others minds.
I’m sure some convoluted fan explanation can be created. Maybe Luke is projecting sensations into people’s minds, and he can project fake images easily but fake sensations of touch are more difficult and have to be limited. There I fixed it.
I just feel that while the movie drops some hints that Luke isn’t really there, it drops others that he is so it’s not just a matter us not noticing the hints that are there.
You don’t have to creat a convoluted fan explanation. You just need to accept that very realistic Force projections can be created, and that it’s very difficult to do so (this one is obvious because Luke dies). Your convoluted fan theory already doesn’t work because C-3PO can see him and he’s not connected to the Force at all.