[SR-14578] Unable to import FoundationXML on Windows - Swift
It's a known issue, that has been fixed for a while, but the change accidentally didn't make it into 5.4. This should be fixed in the 5.5 snapshots, and I hope that we may be able to pull in the fix in a dot-release for 5.4.
As to why the problem exists: CoreFoundation is not meant to be public, and the Windows port has generally been far more aggressive about preventing leakage of internal interfaces and encouraging cross-compilation.