Have you logged into onedrive and gone though the folders that were created when you migrated to it.
When I set up OneDrive on my phone I actually lost a few folders which was super annoying.
I found I didn't like the way OneDrive worked and that it appeared janky and didn't work seamlessly with my phone.
i.e I kept seeing a preparing message at the top of the phone in the status bar.
Personally I've deleted OneDrive and logged out of it and now use Dropbox as a back up.
All the pictures and videos are still in my phone's Gallery.
Current Phone ~Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+ Samsung One Ui 3.1/ Android 11.