What if WiFi is never available any possible way to backup using data?

All the recommended methods require a computer or WiFi.

To learn "How to back up your iPhone, iPad, and iPod touch" click here --> https://support.apple.com/HT203977

I believe 5G is now regarded as reliable enough for iOS updates but there's no reference to it for backing up that I can see.

I don't know if the system will let you get away with using a wi-fi hotspot. Note that this would have all the inherent weaknesses of using a data connection, plus some of hotspot weaknesses added in, which is the whole reason Apple doesn't let you backup over data in the first place.