I am struggling to find up-to-date information on whether or not Dropbox will actually upload photos from the iPhone when the app is in the background. For me it does not.
Old posts imply that Dropbox uses location services to allow the app to run in the background. However Dropbox does not appear in the location services settings (a big no-no if it's actually using location services). Nor is it listed as using location services under Settings -> Privacy -> Files and Folders. I've tried turning off and back on the Background App Refresh, along with iPhone restarts, no change.
Pertinent details: Dropbox set to all photos, background app refresh is on, cellular data is on. Dropbox is added to the Files app. iPhone 12 Pro, iOS 15.2.1. Latest Dropbox app. iCloud photos are turned off. The Dropbox app under iCloud settings is turned off. Dropbox plan is Plus.