I have just come across something odd in WordPress that I have never encountered before. So, I don’t know if it is a new thing or something that has always been there.
I have just set up a new WordPress site and went into change the About page to the Home page. I changed the title and the slug and just click Update, to my knowledge did not alter anything else. I then went into Settings->Reading to change the Static Page to be the Home page but that whole section of the Settings was missing.
After having a long look around to see if this was a new setting in the latest version (5.4) I deiscuoverd that the actually it was something quite different. I had accidentally altered the only page I had (the new Home page) to be Scheduled and not Published so technically there were no live Pages on the site. This is the reason why the ‘Your Homepage Displays’ section was missing.
As soon as I went in and made sure I had at least one live Page that whole section was visible again and I was able to choose the Home page to be the default page.
It’s odd but if you have lost that section, then check to make sure you have a live page because that may well be the cause of the problem.