Hello, you don’t need the Metahuman plugin that’s on Fab to add Metahumans on Mac. At least you didn’t through 5.4 (currently trying to figure out how I can add them in the 5.5 preview to test this out, but that’s another issue*). The Metahumans plugin gives you other functionality with the Metahumans. But up through 5.4 you were able to add them from Quixel Bridge. There are some other plugins it will want to activate once you add it to the project but those are built in and should work.
*Edit to Add: Figured this out. It’s because I hadn’t installed the Quixel Bridge plugin to 5.5 Preview. Oops. I think with the migration I just expected the Metahumans were moving there too. Anyway, that’s what you need to add them to your project on Mac.