Why is my iPhone freezing and shutting down?

So I have an iPhone 12 Pro Max and I've had this problem for about 4-5 days. I first noticed it after I was trying to make some space on my iPhone for a large file, about 12GB in size. So I had deleted some things on my phone and had about 20GB of space free and then the system storage jumped and took up about another 15 GB. Ever since then my phone has frozen in the middle of me being in apps and becoming so unresponsive that it needs to be hard reset. The problem resolved itself for a while and then came back. This time it got progressively worse. It's almost like it was stuck in a boot cycle. It would power on, all my notifications would load in and then it would freeze and shut right back down before I had a chance to open the phone. Well I noticed it was hot. Like hot hot. So I stuck it in the freezer (longer than intended) and to my surprise it was still power cycling in the freezer. Maybe a good 30 minutes to thaw and I was no longer having the issue. I got maybe a full day of use out of my phone and then the problem started all over again but only after being connected to my iMac to be backed up. What is the root of the problem? I've seen faulty battery/connector online but the battery charger fine and holds a charge like it should for a 2 year old phone (it has 88% battery health). I think it's a software bug but I experienced this starting on iOS 15.4 and it continued after getting it updated to 15.4.1

-IG @zay.i0