Failure during official firmware update - phone powered off and won't boot
So, I went to a service and turns out I messed up the PreLoader, that boots the BootLoader. Sometimes this cannot be restored and costs a bunch of money to replace the memory block, but I got lucky and got the phone repaired.

P.S. Do not install official firmware with programs like TWRP, use only your manufacturer's software like, in my case, Asus flash-tool