I was unable to play my old projects and new one too with NP3 in Dorico 4 on a new M1 Mac.
Then I found the following (see Known Issues in Dorico):
Dorico 4 on Apple M1 must be set to operate in Rosetta mode
(the link explains also how to do it). After having started Dorico 4 in Rosetta mode everything’s works fine. Clearly NP3 cannot yet be run as native M1 code, and mixed mode (D4 in M1 native and NP3 in Rosetta) doesn’t work.
Update: Somehow, today Noteperformer has been functioning correctly, even though I haven’t changed anything. I will be content with this as long as the problem doesn’t arise again…