Question: When metainfo is modified is the corresponding file's metadata updated?

Question: When MetaInfo is modified is the corresponding file’s metadata updated? ← assume the file is a FLAC file

No, when you edit MetaInfo via the Rose Connect app or directly on the Rose HiFi device, the changes are not saved to the original FLAC file.
Changes made to metadata are saved exclusively in the Rose device’s internal database (DB).

@joyofmvid

@Grammophone’s answer is correct.
I apologize for the delayed response.