Coming to this a month late, as I just watched the movie and did some searching to see what people thought.

I’m not sure if I totally missed something or people were just reading too much into it, but I didn’t get any kind of trans messaging/interpretation at all. I just thought that Nic Cage was supposed to be a Satanic weirdo (and as you said, I took him as a cis-man). Honestly, Cage’s character being trans didn’t cross my mind at all, I just thought that he was a weirdo.