This app was mentioned in 2 comments, with an average of 0.50 upvotes
Turn on data saver in settings>data. Check to see if you have a limit, where data gets turned off as maybe that's why. Use this to Debloat: https://github.com/0x192/universal-android-debloater.
Try NetGuard firewall to reduce data use and you can block ads.
Switch to open source apps as they have no trackers or ads and usually don't use much data: r/fossdroid, r/degoogle, r/opensource.
Switch to lite apps instead such as Messenger lite or Twitter lite, or use the browser.
Some apps have a data saver built-in such as YouTube but there's NewPipe for YouTube.
Try an app like this: https://play.google.com/store/apps/details?id=com.wefi.wefi
Turn off telemetry: settings>Google>Firebase app indexing>off. Settings>Google>diagnostics>off.
Try using MacroDroid to clear the notification.
On android there is CM sec and CM Free wifi, i don't know why we don't have this on iOS yet.
It detects:
ARP Cheating
Hotspots not having encryption
Hotspots not having adiquit encryption
Fake hotspots
DNS Attacks
MITM attacks
Also detects:
On android they also have We-Fi ( https://play.google.com/store/apps/details?id=com.wefi.wefi&hl=en ) which automatically connects to free hotspots (like those at burgerking and school) , wefi bypasses the login walls.