One very important lesson I learned from over two decades in the airlines is to learn what they want you to learn, don’t waste your time and effort on extraneous material
They will test you on the course they teach you, that’s mutually advantageous and only makes sense
Its very important to remember that each operator does things very differently, studying ‘generic’ or other material / courses from different sources won’t necessarily be helpful, worse it could take you down the wrong path with completely different procedures, that will only be detrimental