How easy is it to learn PS Elements 2021?

There is definitely a learning curve, but you can master it.

Adobe has this available:

Adobe Photoshop Elements Learn & Support

There are also several books  available commercially Go on Amazon or your local bookstore and browse. For example - - Photoshop Elements for Dummies!

If you get stuck, come to this forum for help.

There are numerous resources built into the program.  On the Welcome Screen, there is a carousel of "cards" regarding various subjects.  Some are Try This cards and if you click on them, you will be taken to the appropriate tool or dialog and given visual hints of what to do.  Other cards take you to video tutorials.  If you want to know how to do something, you can type your question into the Search box on the Welcome Screen and you will be given links to relevant information.

Even better are the Guided Edits which hold your hand and walk you through the steps to perform a number of editing tasks, using your own photos.  Here are just the choices for the Basics of editing, but there are many other advanced techniques that are provided:

Of course, there are many other tutorials and how-to videos online but you need to specify that you want Photoshop Elements when searching for them.

And if you run into any problems, you can always come here for some (hopefully) helpful answers.

Added: And if you like to Read The Fine Manual, you can find it here.