I realize that “assertion failed” comes also if stripping the app back to the expo init example, where the app works.
That means I have no logs to go on except “Unhandled JS Exception: Module AppRegistry is not a registered callable module (calling runApplication).” in the phone display.
Ok, after a long day of cutting code base in halves, I found the issue:
“scheme” was missing in the app.json, hence it worked in the expo app but caused an obscure error in the standalone app as a const was preparing a Linking during startup in one file.
I’ll post suggested improvements in the github repo.