Linux is a tool. And I find that the best way to learn handling a new tool is making a project with it.
A book is (maybe) fine, but a project will help you use your knoweldge while you gain it.
So set up a Lemmy/Minetest/Matrix/Teamspeak server or write a bash script to change your audio output device/volume or program a simple bot in your favorite programming language or mix some music or gather a bunch of PDFs and search through them and concatenate them
And while you do that and create directories, change permissions, move files, create users or “cat” or “grep” or “sed” stuff, find out, what every single line you write in a terminal does. And instead of using a graphical program to move files, shutdown your PC or update all programs, only use the command line.