Hi Lacee!
i just ran into the exact same problem myself and from what I can tell the main problem is due to app cache. As far as I am aware the only way to get rid of app cache on iPhones are to delete the app or some apps(not all only like 3 of mine had this) have a built in delete cache button in the app. It won’t completely remove all system data but it should take a large chunk. Just delete apps and reinstall them. Because app cache is included in the “System Data” category. After doing this my system data went from 25ish gbs to 17 gbs.
however I’m gonna be honest with you I think the main issue is definitely your photo storage. Check through your settings because their should be an option like low quality saving or something along the lines of that. Dw it won’t make them like 240p they still look almost identical to the originals but take up a fraction of the storage. I have over like 10k photos but only 1 gbs worth of storage. There’s also an option somewhere where is stores your photos in the iCloud and they still appear in your phone but after a while they get deleted…it’s kinda weird but like their still there just next time you wanna use them your phone would download them from iCloud. Idk if this’ll work for you since well what’s done is done and idk if you can revert your photos. I hope this helped.