This is probably old news, but posting for the benefit of someone who finds this thread in search later:
It seems the 64-bit problem is already solved - the tutotial now reads:
Under "Architectures", set "Architectures" to "Other..." and edit the value to
- For SFML 2.4.2 and earlier: $(ARCHS_STANDARD_32_BIT)
- For SFML 2.5.0 and later: x86_64 and arm64