Lock screen doesn't turn off, possible burn-in?

Hi.

There's a couple of situations I'd like some ask for support, both derived from the same issue. I have an iPhone 13 Pro Max.

• It appears when I turn off the focus feature at night, my iPhone's screen won't turn off when is locked. Sometimes I turn on the screen to see my last notifications before going to sleep, but when I last attempted this I was so sleepy that I didn't realize the iPhone screen remained on for about 6 hours. I would have expected the screen to turn off 30 seconds after last touch activity, but it didn't. Is this a bug or a bad setting?

• After those 6 hours with the lock screen on, I was fearing for some screen burn-in. I already checked with the white and dark grey pictures and I can't seem to find any ghosted or burned image in the screen. So, is it safe? Did the XDR retina display pixels went through the long exposure activity without burn-in? I think so, but I'd like to know your opinion.

Any advice or opinion is highly appreciated.

Thanks in advance.