My wife's 7 plus had the same problem a couple of years ago, and it did indeed turn out to be the front camera assembly.
You can test that on your phone by opening it up and unplugging the front camera. If it then proceeds to boot normally, all you have to do is order a new front camera and replace it and you'll be all set.
Here's the part you need, which you can order with all the tools required to do the repair if you want.
iPhone 7 Front Camera and Sensor Cable - iFixit Store
in order to test whether the front camera will solve the problem, follow this guide up to Step 14, then skip step 15 and complete steps 16 and 17. Stop there, reconnect the battery and fold the screen back over the top of the phone. Power it on and verify whether it boots or not.
iPhone 7 Front Camera and Sensor Cable Replacement - iFixit Repair Guide
As I mentioned, this is what solved the problem for my wife's phone, and given that you've already found indications of problems with the front camera flex cable documented in the phone logs, I'm pretty confident this will fix you right up.
Good luck with your repair, and let us know how it goes!