its unbelievable to me, every few years that i come back to code with IOS, how so many people get stuck with so many issues - just to do simple tasks like compiling code that was previously compiling... or searching where the new settings that Apple want us to tick. and still - fighting and spending hours resolving issues with every xcode new version and ios new updates. so many wasted hours that we could all build other amazing things...

It seems that it is coming from the new field in the target setting - "package name" that was not there in my previous xcode version. It is searching this name as main executable file inside the .app package. This happen only when compiling for a simulator. example: your package was (legacy) "booboo", so it is searching now for booboo.app/booboo, which was not auto generated by the new compile system... someone want to elaborate on that some more?...