I've tried using FME Desktop on one of the new M1-based MacBooks. When running workflows I notice that I get considerably more memory optimization messages and warnings than I do when running on an Intel Mac or on Windows. The result seems seems to be lower performance. I'm not really surprised as it is a brand new platform and Safe probably haven't had time to test this properly. It would be interesting to hear if anyone else have experienced the same thing. I'm also curious to hear if anyone from Safe can shed some light on the matter.
Judging by my tests so far it looks like FME could potentially perform very well on Apple Silicon once the memory issues have been addressed and a universal executable for FME Desktop is available.
For more details and results from running FME workspaces on Apple Silicon (and Intel Macs / Windows) I wrote a blogpost here. I also uploaded the workspace I used for testing.