Can you import metadata from xmp files on Lightroom Mobile?

No, I don't think that's possible as there is no "Read Metadata from File" option in any of the Lightroom apps, only Lightroom Classic has that option. It is possible using the Lightroom Desktop app to import a raw file which already has a corresponding XMP sidecar file containing metadata, and that metadata will be read and applied during the import. But that doesn't work when I tested using Lightroom Mobile on an iPhone 15, the XMP sidecar file is ignored. But if a raw file + XMP sidecar is converted to DNG (thus with the metadata embedded) and then imported into LrM, that metadata WILL be read and applied during the import.