How does APFS on macOS handle upper/lower case file names?
APFS has case-sensitive and case-insensitive variants. The
  case-insensitive variant of APFS is normalization-preserving, but not
  normalization-sensitive. The case-sensitive variant of APFS is both
  normalization-preserving and normalization-sensitive. Filenames in
  APFS are encoded in UTF-8 and aren’t normalized.
  
  The first developer preview of APFS, made available in macOS Sierra in
  June 2016, offered only the case-sensitive variant. In macOS 10.12.4,
  the APFS developer preview was updated to also include a
  case-insensitive variant. In iOS 10.3, the case-sensitive variant of
  APFS is used.


Apple’s Developer FAQs