Update 14 August 2023 - MAME (current) was also updated to version 0.257 and is on par with official MAME as of this blog update
Recently the iOS core also was slimmed down to 77 MB - still a lot compared to the 9.2 MB that FBNeo brings, but nevertheless some improvement.
With the latest tweaks, the MAME (current) Core is functional on Mac RetroArch, but still has some issues. As of this writing, the „current“ RetroArch core is version 0.251, whereas official MAME is already at version 0.255. In practice, this probably won’t matter that much to you.