The Save Metadata To File command doesn't always update a photo's metadata status to indicate it is Up To Date. To reproduce:
1. Download and open this catalog in LR:
https://www.dropbox.com/scl/fi/jokv9a8pfsdc2z0jrqlu5/save-metadat-bug.2024.05.25.zip?rlkey=z833g3ek2...
2. In Library View > View Options > Grid View, check Cell Icons > Unsaved Metadata.
3. In the Library Filter bar, open the Metadata browser with the column Metadata Status.
4. Observe that all 32 photos have metadata status Has Been Changed as indicated in the Metadata browser and on the thumbnails.
5. Select all the photos and do Metadata > Save Metadata To File.
6. Observe that 32 photos remain with status Has Been Changed, and Finder / File Explorer show the files or their .xmp sidecards have their Date Modified set to "now", indicating that LR wrote the files (but I haven't tested if they've been written correctly).
Tested on LR 13.3 / Mac OS 14.4.1 and Windows 11.