
Hi Leah. Pick a single cloud to be the source of truth and turn on auto backup everywhere. If you are in the Apple world and enable iCloud Photos on iPhone, iPad, and Mac. On iPhone go to Settings > your name > iCloud > Photos and enable Sync this iPhone, and on Mac open Photos > Settings > iCloud and turn on iCloud Photos. If you are mixed platform, use Google Photos and in the mobile app open your profile photo > Photos settings > Backup and turn on Backup. On Android toggle only Camera in Backup device folders to keep screenshots out and stop manual AirDrop or USB imports once sync is running.
Do the initial dedupe after everything finishes syncing. Apple Photos shows a Duplicates album that lets you merge exact copies, and Google Photos has Library > Utilities with Duplicates suggestions, though it may not appear for every account. For tagging, enable face grouping in settings, then name people in the People album and merge lookalikes. for places, keep camera location on and batch add a missing location on Mac by selecting a set, pressing Command I, and entering a city once. Tame screenshots by creating a Smart Album on Mac with Media type is Screenshot and Date added is in the last 30 days, then delete that set monthly. on Android just turn off Backup for the Screenshots folder. Backups should be automated, so if you use iCloud choose Download Originals to this Mac and let Time Machine back up the Photos library to an external drive, and if you use Google Photos schedule a Takeout export every two months and copy the zips to a drive.