Hi!
Pixelmator Pro explicitly points you to Apple’s 'Digital camera RAW formats supported…' list to determine what RAW formats you can open in the app, which strongly implies RAW compatibility is gated by the operating system. Apple also describes that list as system-level RAW support in iOS, iPadOS, macOS. On iPad, iPhone, the Pixelmator team has also stated they rely on the iPadOS native RAW engine and can’t add new RAW format support themselves until Apple adds it.
- Your camera body may appear as 'supported' in the app’s marketing,support matrix, but your current macOS, iOS, iPadOS version may not actually include RAW decoding support for that exact camera (or for the way your camera is currently writing CR3 files).
Convert CR3 > DNG using Adobe’s DNG Converter