Honestly, in my opinion/my experience the best way to learn linux is to (1) just jump in and start using it and (2) being patient with yourself while you adjust. Nothing makes you quite as comfortable with using an operating system like using it every day, even if all you do is boot it up, open a web browser and watch gifs of cats on the Internet. When I was making the switch, it was invaluable to just be in there, using regularly. Second was also to be patient with myself. I found, at first, that i was getting frustrated when I needed to troubleshoot something because I was so used to the Windows way of things. I had to give myself time to learn and adapt.

It depends on what you are trying to learn. If it's just using it as a desktop then it's more a matter of just using it for a while to change your muscle memory from Win or Mac.

If you're looking for more of a command line/server experience, most distros have excellent documentation. This may be a minority opinion, but I personally like Oracle Linux (a Red Hat clone) and their documentation; https://docs.oracle.com/en/operating-systems/oracle-linux/index.html

I also like FreeBSD which isn't technically Linux but very similar in a lot of regards. They also have excellent documentation; https://docs.freebsd.org/en/

Ultimately, which distro you wind up liking is entirely subjective and one of the great aspects of the open source world. Oracle in particular you may see a lot of hate towards, but I've always had good success with their products and support. Best of luck!

Just install yourself a Linux and search the web when in need 🙂