That’s correct. It’s a BETA for developers only, not regular users, to test compile their plugins against an ARM version of Rack, on Apple Silicon, to see if it works, get feedback and prepare for an eventual release of Rack on ARM with all plugins working in the library. So for regular users: Don’t use it or report problems with it, it’s only for developers and/or deeply technical people.
Quoting from Rack development blog - #85 by Vortico :
Builds of Rack for Mac ARM are available for developers to build and test their plugins on Mac ARM. This is in “beta” stage, so some features or plugin adapters might not work correctly.