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!
We have a 15 year old who started recently. Once we found the correct dosage it made a huge difference in his overall behavior. I found the testing to be trickier than administering the insulin. Ultimately I settled on the tester below, and found it easiest to get the blood sample from the ear tip. After about a week, we developed a good system for the testing as well. Best of luck!
AlphaTRAK 3, 8 Piece Pet Blood Glucose Monitoring Kit for Diabetic Cats and Dogs, All-in-One Solution for in-Clinic Or at Home, with Digital Results https://a.co/d/gvL9AcS