A single page in the root of the site (a leaf bundle is also a single page) has:
Type = page
Kind = page
Section =
Which means you cannot place its single page template in a layouts/about/ directory and expect it to work.
https://gohugo.io/templates/lookup-order/#hugo-layouts-lookup-rules
Do this:
+++
title = 'About'
date = 2022-12-08T07:36:59-08:00
draft = false
layout = 'about'
+++
The lookup order will be:
layouts/page/about.html
layouts/page/single.html
layouts/_default/about.html
layouts/_default/single.html