This is my bad again, I thought I’d pushed up arm64 support earlier after adding it, -.- sorry about that.
If you get the latest changes on my hxcpp patch branch HXCPP_ARM64 will now work. haxelib hxcpp update should do it, but you can also cd into the hxcpp git directory and do git pull. †
As for VALID_ARCHS, you’re right and I wasn’t reading thoroughly enough, seems like you can exclude architectures instead or enable ONLY_ACTIVE_ARCH: Xcode 12, building for iOS Simulator, but linking in object file built for iOS, for architecture arm64 - Stack Overflow
† I’m not happy with hxcpp’s current approach of requiring new architectures defined in the config before they work so I’ve also added a new flag so you can set whatever arch you like with -D HXCPP_ARCH=arm64. Opened an issue and will work to make this work on all targets in the future (current added for watchos and watchsimulator)