Watch / listen to “If The Emperor had a Text To Speech.” It is a really good non canon primer for the world. It wasn’t made by GW, and so the creators abandoned that series a few years ago when GW changed their licence agreement.

It is about 90% canon, as in, if the Emperor could routinely talk to anyone, he would start unfucking The Imperium, post haste. The current Imperium is nothing like what he was trying to make.