I was able to get a fat binary if I did build using the command line tool of xcodebuild and pass it basic arguments and add each architecture there. Weird.

Yep. Spent last 4 hours trying to figure out why 16.1 won't build FAT binaries. Architectures asked for set to x86_64 arm64 But the binary when tested with lipo says is only arm64. OUCH!