I'm glad I found this post. I am heaving the same issue on my iPhone 12 Pro. I thought is a hardware issue, I had a case with Apple, and someone looked at it at Apple store. They said they would ned to send to the lab to investigate, but my phone was within 15 days of receiving it, so I just replaced it with Rogers, since I bought through them.
The problem is that I am having the same issue on the new one too. It's true that first time I opened up, I brought my old phone, iPhone X to sync it and all my apps and settings got copied over. I am not sure if that affected it and if the issue would have been there if I just set up as new and not copying over any settings.
I tried a firmware upgrade to 14.4 first, that didn't fix it, and I tried to erase my phone from settings and using computer too by downloading the whole OS again, but that didn't fix it either.