iPad mini 2 cellular ios 12.5.5 - not working correct after restoring

Hi !

im still using my ipad mini 2. Device stoped support at iOS 12.5.5 and everything is working properly until Restoring device.

(First of all -restoring is mostly not going well, need to make it severel times to make it finish)

After succesfull restoring apeers Hello screen. I choose language and region, when i want to choose wifi connection, the keyboard is not showing (i choose no wifi option) after few more steps ipad is completing setup and sudeenly is rebooting to the start over again. In this secound Setup all setting is working well, so I can finaly finish and start using ipad.

After succesfull setup i find that power button is not working, in display setting there is no lock/Unlock option for case and App Store is not downloading apps (i can login to icloud even Files and Photos can synchronize)

Maybe more features are not working properly but didnt findout yet.

Only way i can use iPad right now is to restore backup before recently first restoring. What is happening? Is Apple making old devices useless on purpose? Maybe this restoring version of ios 12.5.5 is not compatible?

Very confusing issue and hope to find help.