IOS XR primer

And of course, the Master Command Listing for IOS XR was
very helpful too.

Once you have all this down, you can then dig into specific
topics such as RPL, e.t.c.

Here is a good one on RPL.

gives a baseline with some good info as to differences

and then move on to

which gives the in depth topic by topic.
Document tab as well as Blog tab will get you expert at IOS-XR in no time.  pop “IOS-XR” into the search