Likely, you damaged the firmware there’s a reason it said not to turn off, you will have to reinstall the bios, you can try unplugging battery and cmos battery for 30 minutes to see if it auto resets otherwise you’ll need to install a new firmware
I had this same issue solved it by freezing the motherboard, I took the battery out and got the motherboard below operating temperature, where it would say you’re iPad needs to warm up before turning on, than restored it, it worked for me but best of luck and I hope it works for you as well,
Idk what for that specific situation beside a new motherboard a1778 specifically, but I had the audio ic died with an a1778, I was able to fix the issue with duct tape believe it or not I was able to apply pressure to the chip and was able to fix it and got it working perfectly now it’s been 6 months
I recently took my MacBook into the apple store, I showed them the site and they said it’s not as big if a deal as people are making it and want 475 for the repair. I declined the repair price. I still have a broken MacBook and we can see apple truly doesn’t care
I don’t know if anyone has said this yet it is actually possible to upgrade the ram very easily, all you have to do is find a motherboard on eBay that has 16gb ram and install it
you can find it for about 15 bucks on amazon