Trying to use the $validate function on macos, doesn't seem to be evaluated and simply adds $validate( to the file path.
Is it supported, and if so how can I get it to work like on Windows?
The configuration setting Replace invalid NTFS characters at Preferences → General → Filenames might be what you're looking for.
If enabled, characters that are not allowed in Windows NTFS filenames are automatically replaced by an underscore
_on field lookup. The following characters are replaced:\ : / * ? < > | ".
Enabling the automatic replacement also prevents folder creation when using the converter Tag - Filename with fields that contain the forward slash character
/.