As far as I'm aware, Redlib gets around blocks in two ways. The partially implemented client-side blocks I presume are by just stripping the code (e.g. seeing the post but it's greyed out and has a popup saying "sign in" in front of it, or when your whole screen is a login page but all the actual content was already loaded in the background, deleting that code means you can read the post just fine)
And the rest is just tricking Reddit by mimicking the request format & behavior of the Android Reddit app, which tricks Reddit into believing the user is supposed to be allowed access or shouldn't be rate limited, because obviously anybody using the app is a real signed-in user... I guess? (this information is from their GitHub page's README but I'm not sure exactly how all this works under the hood)