Malfunctioning Power Button

I'm starting this new question as the last Power button related one is over a year ago, and there are some differences to that.

So about a year ago, I noticed that the Power button on my 1st gen iPhone SE became unresponsive. That is, it won't do anything when pressed. You can press it down, so it isn't jammed. It just won't do anything. Visual inspection of the Power button shows no dirt/debris. I tried to hard reset/shut down the iPhone (by going to Settings>General>Shut Down, then plugging in the charger), but that didn't work. The Power button was still unresponsive to presses. Since I can wake the iPhone with the Home button, and then set the screen to wake when raised, I didn't bother much with it nor did a factory restore.

But after updating to iOS 14.3, some thing weird has been happening. I'm not sure if it's relevant, but during the update to 14.3, I got the support.apple.com/iphone/restore screen. I was doing the update through iTunes on my Windows 10 desktop. I followed the instructions from the website about Reinstall iOS, because iTunes had a message that said something along the lines of "error during update".

Anyway, after successfully reinstalling iOS and restoring the Back Up (thank you for automatic back ups during updates, as I forgot to do that manually), the iPhone seemed fine. Even the Power button became responsive again (hurray?). Until 3 days later when I started randomly getting Power button behaviors, such as the screen waking without anyone touching the iPhone, or just getting the Shut Down Slider as if the Power button was long pressed, but my fingers were away from the button or even when the iPhone is just on a tabletop.

I first noticed the behavior (getting the random Shut Down Slider screen) while I was using the Pages app to be a prompt while making a lecture video for my online class. Then later, it repeats on random while I'm just using the phone on various apps.

I've tried to turn the iPhone off and on by long pressing the now-funtional-again Power button. But after a few minutes with the iPhone just lying on the desk while charging, I see the Shut Down Slider on the screen.

Apologies for the long winded question, but I wanted to put in as much details as possible. Any ideas as to what's going on and what to do?