The Garritan support website and forums are a huge mess and I wanted to provide some details about running Garritan CFX on Apple Silicon. There was recently some information about Garritan supporting Apple Silicon:
https://makemusic.zendesk.com/hc/en-us/articles/1500003504881-Finale-Garritan-Compatibility-with-Apple-Silicon-M1-
According to that page, Apple Silicon is supported natively for Garritan CFX but only if you run it through the Aria Player* and not through the standalone Garritan CFX app which still runs through Rosetta 2. In my experience, running Garritan CFX through Rosetta 2 translation is quite good but not entirely problem free and I get occasional glitches. Now, it's important to note that running Garritan CFX through the Aria Player instead of its own standalone player won't provide all the features of Garritan CFX. I'm not sure what exact features are missing though. I think it's the convolution reverb that is missing (which is totally fine with me) but there may be other missing features, let me know if you have that information (P.S. There's a problem when playing many notes with the sustain pedal, see below). Now, on that page they also provide a link for downloading the Apple Silicon native Aria Player, however when I downloaded it and ran it, I got an error which other people also experience “Garritan ARIA Player Cannot connect to engine, please re-install“:

I tried reinstalling it and whatnot but without any success and Garritan are not responding to people that have this problem. After a lot of searching on the Internet I actually found another Garritan page that describes how to fully uninstall the Aria Player:
https://makemusic.zendesk.com/hc/en-us/articles/217750048-Uninstalling-the-ARIA-Player-and-ARIA-Engine-
I followed it, however on steps 6 and 10 where they ask you to delete the entire Garritan
folder I didn't do that because in that folder there are also the Garritan CFX installation files and deleting them will mess it up and you will have to reinstall it, so instead I expanded it and deleted only the Aria Player sub-folder.
After that I restarted my Mac and installed the Apple Silicon version of Aria Player from the first link (as of now it's 2.0.0.1) and voila. Now the Aria Player runs natively, I can open the Garritan CFX sample inside and play with insane performance without any glitches. I hope that helps people who are struggling with the same problem.
*Aria Player is a sample player that comes with the Garritan CFX installation as a separate app along the main Garritan CFX app. To my knowledge the Aria Player can be used for loading various other SFZ instruments besides Garritan CFX. It's similar to Kontakt, just different format of samples. Most people will use the standalone app and thus will not be aware that they also have the Aria Player installed and can use it alternatively to load and play Garritan CFX. It's only the Aria Player that is Apple Silicon native as of now.