There's generally more information associated with the thermalmonitord failure. It will help if you post the first page of your panic log so we can see which particular sensor is missing, because that's what you're looking for. There's more information on the subject in @flannelist's excellent kernel panic wiki page.
Using that information you should be able to pin down which part needs to be replaced to fix the issue you're seeing based on which sensor is missing. My personal guess is that you're going to find that you're having an issue with the lightning port flex cable because that's the part that's most easily exposed to liquid submersion. Of course, if you've got any cracks on the front or back of the phone then all bets are off.
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=== Update (11/27/23) ===
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Yep, here's the smoking gun right there.
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[quote|format=featured]
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Missing sensor(s): Prs0
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[/quote]
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PRS0 is the barometric pressure sensor located on the lightning port flex cable assembly. It's connected to the barometric vent, so any failure in the seal of that vent means the sensor gets exposed to water and - as you found out - it fails. Here's the part you'll need to replace to fix the sensor.
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[product|IF442-010|iPhone 12/12 Pro Lightning Connector Assembly|new_window=true]
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Note that it comes in different colors in order for the inside of the port to match the color of your phone. That's strictly a cosmetic issue though; in practice you can put any color you want in there. You can buy it here on iFixit and support their repair efforts, but you can also find in on the major sites like Amazon, eBay and AliExpress among others.
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Unfortunately, iFixit doesn't have a guide for your repair, but there's a Spanish site called Nadie Me Llama Gallina that has just what you need. This guide will step you through the replacement from beginning to end.
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[link|https://www.nadiemellamagallina.com/en/manuales/smartphones-1/apple-5/apple-iphone-12-1241/flex-de-carga-11058|Manuales / Apple iPhone 12 / Auxiliary board|new_window=true]
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Don't forget to pick up a sheet of precut adhesive to secure the screen back on once your repair is complete; although it won't restore the IP68 rating, it will help keep water out should it get accidentally exposed. To be honest, I usually buy a couple; they're unfortunately all too easy to mess up - if you don't get them on exactly right the first time there's no second chance.
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That should do it for you; once you've replaced that part your phone should be back in business! Good luck with it, and let us know how it goes.
Hi Bernie,
There's generally more information associated with the thermalmonitord failure. It will help if you post the first page of your panic log so we can see which particular sensor is missing, because that's what you're looking for. There's more information on the subject in @flannelist's excellent kernel panic wiki page.
[[iPhone Kernel Panics|iPhone Kernel Panics - iFixit|new_window=true]]
Using that information you should be able to pin down which part needs to be replaced to fix the issue you're seeing based on which sensor is missing. My personal guess is that you're going to find that you're having an issue with the lightning port flex cable because that's the part that's most easily exposed to liquid submersion. Of course, if you've got any cracks on the front or back of the phone then all bets are off.