Bootlooping after modification/repair

A few years ago, I modified a iPhone XR and put it inside a custom housing to make it look like an iPhone 13. I used almost completely all the original parts except for a new screen and the custom housing. It was functional for quite some time, but is now stuck in a boot loop that is not fixed by restoring or updating using Finder on my Mac. What hardware or software issues can I rule out and what steps are next for diagnosing this phone?

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crwdns2889612:0crwdne2889612:0 0

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I also noticed a small tear on the flex cable to the screen. Could that be part of the issues even though I can get it into recovery mode with the screen working?

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I tested it with the original cracked display and it still boot looped...

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