iPhone 11 Pro - boot loop with error 4013, solution without data loss

Not a question, re-posting a below solution from emilyylauren for a boot loop error issue.

I had an infinite boot loop error, which turned out to also be from a small amount of water damage near the ear speaker from wear and tear and humidity. This was confirmed by the Apple Genius Bar, who opened the iPhone and could see the red moisture indicator. I followed the below steps, and also kept the phone in rice for a number of days to fully dry out any moisture. And the phone worked again! I then immediately backed up and transferred to a new iPhone. Thank you so much for the invaluable knowledge below, it gave me peace of mind that all was not lost while trying to sort it out!

“Twice in the last two months, my iPhone XS suddenly shut down and entered an infinite boot loop sequence after using my phone at the gym to play music. Much to my dismay, entering recovery mode and connecting my XS to my MacBook to update/restore produced a continuous error 4013. Of course I did not have more than the basic iCloud storage plan, so I did not have any recent backups. I was at risk of losing thousands and thousands of photos and personal memories.

After many, many hours trying to research viable solutions without opening the phone, I have been able to piece together my own solution based off info from various forums.

It seems the boot loop and error 4013 on these particular devices are a result of sweat or other form of liquid getting into the earpiece. Many others have mentioned opening the phone and disconnecting the earpiece flex cable. This works, but disables Face recognition. Personally, I am on a contract with my carrier where you bring back the device in good working condition at the end of the agreement, so this was not an appropriate solution.

The first time this happened, I tried over and over to update/restore the device on my Mac to no avail. After around 5-6 hours it finally came back to life on its own. The second time this happened (yesterday) the phone never started working again, so I ended up leaving it in rice overnight (silica gel could also be used). It still didn't quite do the trick, as I connected my iPhone to Mac and tried updating again without success. This time, it got through the software update, and half way through "attempting to recover data", but shortly after it did not complete the data recovery and went back into boot loop mode.

After watching this video ( https://www.youtube.com/watch?v=Tqmy6bmHjRY ) the repairman mentioned the earpiece area likely still has some liquid inside or is damp. He took the phone apart to repair but had also used an air compressor before opening the phone and blew it into the earpiece for a few minutes.

I decided to replicate this method using my hair dryer, on cool setting and lowest power and held it against the earpiece for about 2-3 minutes to attempt to dry out any remaining moisture. After one or two more failed attempts to connect on my Mac it started the software update and successfully completed the data recovery. Finally after 24 hours I had my phone back, and running as normal. I have been able to complete a back up as well.

My advice is to use a gentle form of air flow and hold it to the earpiece for a few minutes to encourage any remaining moisture to dry. I'm posting this for any others who've encountered this problem and don't have the option to pay for repairs or open the phone.”