Before reading you have to know that I'm playing train simulator on a 11-years-old Apple-Notebook with Windows as a virtual machine. A few months ago I bought Munich-Garmisch. But it had a big problem: After a few kilometers the FPS was pulled down to 10 and a few seconds Train Simulator didn't work anymore and an error code appeared. First Windows said 'out of memory' and I should reinstall the DLC.I ignored that and tried it with the 64-bit-edition and other things. But after a month I reinstalled it. But it didn't help, train simulator always crashed. I don't know what the problem is because train simulator doesn't has this problem with routes like Munich-Augsburg or the 'Mittenwaldbahn' whiches have the same requirements. If there are any mistakes in my English I'm very sorry for them because normally I speak German.
Maybe, that I can help you. I'm also running TS2021 on M1 MB Pro, also with Windows as a virtual machine (in Parallels Deskto. Recently I have purchased Munich-Garmisch route and I have the similar experience as you. After a few kilometres (e.g. shortly after departure from Garmisch, or shortly after departing Pasing in direction to Starnberg) the game has frozen and TS fell back to Windows. I have found some workaround for it. I unpacked the .ap file in RailWorks folder in directory \Assets\RSC\MunichGarmisch (this can be done e.g. with 7Zip). Then I have placed the unpacked content back into MunichGarmisch directory, and moved the .ap file away. After some checking with other routes using these objects too, I have found that there is some problem in subfolder Scenery\Procedural. I have moved to another directory outside of TS all files between fence_3d_styleA.bin and gen_hedge02.XSec (there are some fences and so on...). OK, now there some objects missing, but it has not affected the visual appearance. Anyway now I can ride the whole route from Munich to Garmisch.
The fact you are running the route using a method that is not supported is not a problem with the route. It works fine for people who use Windows as the base program
