This tutorial doesn't run on my version Blender 4.0 or 4.2 at all. Can't follow along with the steps at all.
Here's the link to that course but in 4.2 version:
https://cgcookie.com/courses/core-fundamentals-of-texturing-in-blender
But remember, if you want to follow along in old courses, you can download that version of Blender in which the course was made.
I'm pretty sure that there isn't much difference between 2.9 and 4.2 as far as UV unwrapping goes. I'm curious as to which part you can't do? In 4.3 they rearranged the menus and made changes to how the smart UV works, but most of it is still the same. You just have to do a little hunting to find the options. There were additional options added to UV Project in 3.6 and support for non-square images.
What you could do, is to first watch this Course with 2.90 and after that, watch the 4.2 Version of the Course (CORE) with 4.2.
Texturing is quite complicated and watching it twice, explained in different ways and also in different Blender Versions will be really helpful.
That being said, the 2.90 Course is by Jonathan Lampel, who has had a lot of experience teaching Blender and the new Version by Ewa Wierbik-Ziąbka is one of her first Courses, and also made under great time pressure.