What does warning "Mapping architecture arm64 to x86_64" mean?
I was able to silence these warnings by changing my Valid Architectures setting to $(ARCHS_STANDARD) which matches my Architectures setting as well.
Oddly, this displayed as armv7 arm64 (in comparison to the default setting of armv7 armv7s arm64), but setting it to that value manually still caused the warnings. Not sure what the significance of that is, but I haven't noticed any problems in my testing yet.
You likely have the VALID_ARCHS ("Valid Architectures") build setting overridden, either for the target or for its project. This is a build setting that should get its value automatically based on which run destination you're building for. When you figure out where this override is coming from (the build setting will display in bold when overridden), select it and hit the delete key to restore it to the default value.