Honestly, i'm still kinda figuring out all the deep system stuff myself, but you definitely wanna back up more than just photos. If you use Samsung Smart Switch on a computer (it’s free!), it basically clones your home screen and settings so you don't gotta spend hours setting it back up. One big thing—make sure you know your Google password or even remove the account from the phone before the reset... i've heard of people getting locked out by 'Factory Reset Protection' and it sounds like a nightmare. For app data, it’s tricky because not every app saves progress to Google Drive automatically, so you might wanna check individual settings for things like WhatsApp or games. Does your Wi-Fi usually act up? Usually, a fresh start fixes that stuff, but maybe write down your Wi-Fi passwords just in case since those dont always carry over. Tbh, using the PC version of Smart Switch is the best budget move since you dont gotta pay for extra cloud storage or Samsung Cloud subscriptions. Is it possible to just copy the 'Android' folder to a thumb drive too? I've seen some people do that for extra safety...

Yeah, definitely agree on the settings part—nothing is more annoying than having to re-map every single notification sound and vibration pattern from scratch. Honestly, I’ve learned the hard way that the biggest headache isn't always the photos, it's the random stuff that isn't synced automatically. One small thing to add: check your 2FA or authenticator apps. I once reset my S21 without thinking and it took me like three days of emailing support teams to get back into my accounts because I lost my login tokens. It was basically a nightmare, tbh. Since I'm always trying to save a buck and avoid paying for extra storage, I usually just do this: * Plug the phone into a laptop and manually drag the entire 'Downloads' and 'Documents' folders over.
* Take screenshots of my home screen layout so I remember where I put everything.
* Verify that my banking apps don't need a 'de-registration' step before moving to a 'new' device. It's a bit more manual, but I've found it's the only way to be 100% sure I didn't miss some random local file.

Finally someone says it. Ive been thinking this for a while but wasnt sure.

Honestly, if you want total reliability without stressing over cloud sync issues or slow wifi, just go local. I always use a SanDisk Ultra Dual Drive Luxe USB Type-C 128GB to dump my heaviest files and app data backups directly. It is way faster than waiting for a slow upload and you know exactly where your stuff is. Since Samsung moved away from their own cloud for photos, you should really look into Microsoft OneDrive 1TB Personal Plan because it integrates natively with the S21 gallery now. It handles the sync much better than most third-party apps. For the login headache, grab Bitwarden Password Manager Premium or even just the free version... make sure you have it logged in on a laptop or another device first so you can check your passwords while the phone is wiping. It'll save you from that 'incorrect password' loop when you're trying to set everything back up. Just makes the whole process way less stressful tbh.