Phone not connecting to data or establishing internet connection. How to fix?
Does this happen in one location or everywhere you go to ?
If in one location then please check your mobile networks masts via any available network checker option they provide.
If everywhere then as a process of elimination can you try your sim card in another phone and another sim card in your phone to rule out the phone and or sim card.
If your experience is the same in another phone then your sim card may need replacing.
If it turns out to be the phone then I'd suggest to use a Samsung Experience Store or Samsung Service Centre to have a diagnostic test on it.
Current Phone ~Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+ Samsung One Ui 3.1/ Android 11.