To motivate work on writing this tutorial, it should ideally offer something different to (but not necessarily better than) all preexisting resources.
Various resources were suggested in comments at https://www.reddit.com/r/PHP/comments/f5ix6n/anyone_know_a_good_php_as_a_second_language/ :
See intro.
Looks like it covers a lot of the same stuff I want to cover, but with different approach. Most obviously this will be a text based tutorial for readers to use at their own pace, not a series of videos. Laracasts covers mixing HTML with PHP which I plan to skip. Doesn't use strict types in code examples. Final section is about Laravel, which I disprefer. I don't plan to include anything on how to use a framework but will include something about them in a 'what next' section at the end, perhaps including links to https://symfony.com/doc/current/setup.html and https://symfony.com/doc/current/create_framework/index.html
Although the course is free the Laracasts website has lots of paid content, and the site overall feels quite focused on selling subscriptions.
Video at https://www.youtube.com/watch?v=7TF00hJI78Y
Video is old - from 2014. Again mixes PHP and HTML.
https://learnxinyminutes.com/docs/php/
Again this is not focused on contemporary PHP - it "describes PHP 5+". I want to describe PHP 7.2+, if I don't decide to just do 7.4 only. I do like the terse format - very quick to read through, but this is aiming to a be a bit gentler.
See intro again. Tutorial part is much too minimal, docs as a whole go into much more detail than desired here.