With the release of Big Sur imminent: MM's last official post on compatibility for Garritan claims:
"macOS 10.15 Catalina is not considered within the system requirements for the Garritan Instrument libraries ... we are currently unable to provide support for Garritan libraries on this OS.".
And yet Finale 26.3, which contains the ARIA Player and Garritan samples, is given a clean bill of health. And the only known issue listed related to the installation of CFX Piano.
It's pretty poor that no further statement has been given, just as Catalina's year is up. The ARIA Engine was updated in November 2019 with listed fixes for 'some files not opening on Catalina', and a further update was released this year in June.
I guess MM's statement on Big Sur will be released soon. It will be interesting to note if they say anything about Garritan stuff.
My own experience is that the latest updates of ARIA Player and Engine work with no problems at all on Catalina and later.