How to reduce system data usage on iPhone 12 mini?

My issue is that my iphone 12 mini has over the last 6 months inflated system data usage from 18-22 gb to literally 38. No amount of date tricks, cache clearing, deleting of messages, photos, or apps help. Every time I delete photos, messages, downloads, all the space i make gets filled with system data. Ive deleted around 5 gigabytes of photos and videos, 5 gigabytes of messages, I have no extra apps, no emails, NOTHING. I simply cannot seem to find an end to the accumulation of system data. I should have at LEAST 15 if not 20 gigabytes freed from all the cleaning up Ive done on the phone. Is this just the slowing of software that older phones experience as newer ones come out?? I dont see it worth getting a new device over.My phone shuts off and restarts randomly and its losing function and doesnt stop until i delete more stuff before briefly filling itself up again.

[Re-Titled by Moderator]