There are several great mods out there, and I just wish to give a shoutout to these mods that I really like to use while I'm playing with this mod.

The first one is "Bibliophile" that adds a lot of interesting historical books and artifacts. It's a really great and popular mod:
https://steamcommunity.com/sharedfiles/filedetails/?id=1478492075&searchtext=bibliophile

The second one is "No Interreligious Defensive Pacts" which prevents realms of different religious groups to band together in a defensive pact. This means all christians will band up against you (as a christian) if you conquer a lot and keep attacking other christians, but they will not intervene to stop you from conquering Jerusalem from the muslims. In my experience this also makes the mongols conquer a bit more since christians won't interfere with mongol conquests of muslim Persia.
https://steamcommunity.com/sharedfiles/filedetails/?id=1522115176&searchtext=no+interreligious

The third one is the Art Replacement mod:
https://steamcommunity.com/sharedfiles/filedetails/?id=575946499&searchtext=art

The fourth one is Chinese Caliphates, which adds religions in China. These may shift during the game and you may even send missionaries to spread your faith in the Middle Kingdom. Needless to say, the mod adds a lot of immersion to the game:
https://steamcommunity.com/sharedfiles/filedetails/?id=1826064398&searchtext=

The fifth is Ceasar's Wonders:
https://steamcommunity.com/sharedfiles/filedetails/?id=1829453519

If you want the nice settlement pictures from Immersive Religious Holdings:
https://steamcommunity.com/sharedfiles/filedetails/?id=2070148372
then you also need to use this compatability mod: https://steamcommunity.com/sharedfiles/filedetails/?id=2116983370

A submod adding some content for early starting dates:
https://steamcommunity.com/sharedfiles/filedetails/?id=2736624893