There’s lots of good stuff in the 1.9.21 beta, but at this point you can skip the beta because it will be shipping soon.
The slowness in your previous post had nothing to do with Rosetta. It was because your library was offloaded from the Mac and had to be downloaded from cloud storage.
I’m not sure what the “to” is referring to—errors go the other direction from macOS to EagleFiler. But, yes, it does include improvements to the error handling.
Yes.