Why does my iPhone x boot loop after the new update

so i just bought an used iphone 10 and it had no issues whatsoever. i tried to use the memoji for the first time but the phone froze and then locked and it was stuck on the lock screen and i couldn't do anything. i was panicking and didn't know what to do until i decided to open the phone and disconnect the battery. then i reconnected the cable and turned on the phone but once it turned on i saw the face id disabled notification and i was like it's not a serious problem. the phone had no problems but after a month it gave me an update so i downloaded it and tried to install it but the phone couldn't turn on after the update and it was boot looping. so i put the phone into the recovery mode and tried itunes to install the update but still unsuccessful... it couldn't finish the update and gave me the error that you must restore this iphone. A repairer told me it's a logic board problem and I'm dying. just tell me it's fixable.