I raised, flagged, liked and did everything I could on the support forums to get the Photos GUI to report somewhere whether an image was backed up in Original or "High" quality. It went nowhere. And last I checked it was still impossible.
I now treat Google Photos as a last resort approxi-backup and do all my own offline backups to a HDD because I can't trust the metadata. And I'm one of those idiots who even pays for Google One.
(seriously, would a tag like "quality:original" stump the engineering team?!)
Edit: Ha! It's set back to "High" for me AGAIN!