iPad Not Powering on - Charger weird readings

Hello everyone.

My iPad Air 3 stopped working. I then found out that the display was defective and replaced it. After that, it fully boots up once. I let it charge to about 80% and then turned it off. Now it doesn't work anymore. When I plug it into the charger it shows 5V and rises to 2.2A charging power and then drops to 2V and 0A only to then rise again to 5V 2.2A. This repeats itself endlessly.

No Apple logo or anything like that appears on the display. I've already tried a reset via power + home button.

Board looks clean so far, nothing gets hot when the charger is on.

Any tips ?

Thanks and Greetings