So I invited Caliph's brother Sa'ud Abbasid, convinced him of foolishness of his silly religion, and pressed his claim, all while hopefully derailing the jihad for Africa.
Weirdly he was in matrilineal marriage (game rules mess with Muslims), and his heir was an Uyghur Zoroastrian girl. I arranged for her to marry an illegitimate bastard of my second daughter, and bribed her to come over as well and accept a more reasonable religion.
But there's a war to fight - I sent my troops to Egypt, and I got individual stacks on their way to jihad target. And conveniently every province there has decent supply and river defense bonus from basically anywhere.
Annoyingly a host invasion launched in the middle of our war, but host sizes are capped, so it was not major trouble.
After this great victory, I thought caliphate was over, but no - even though caliph had almost no legit vassal levies, you can keep already raised levies as long as you'd like, so he still had 20k to press on jihad. And thanks to these scary looking troops, his brother folded to his independence faction, and let him and two other dukes go.
So now caliph got himself a mid-sized country, when I hoped it would be eradicated.
I even tried to help the Aztecs by asking them to become my tributary, but by the time they accepted jihad was at 95%. Oh well.
Meanwhile, Vlach Orthodox count of Naissos got 22k event troops, which didn't even seem like much nowadays, but he conquered himself a nice chunk of land. With some luck, it could end up as a small resurgent Byzantine Empire, same as emir of Granada got himself half of Andalusia become Francia stopped his attempts.
Oh and on subject of my (now dead) husband becoming doge of Genoa - it currently has 4/5 patrician houses "de Genoa". I suspect something glitched there, but not sure what, and I don't recall ever seeing this before.
With so much gold and no free holdings, I started building universities - first in my demesne, then just outside, so technology can spread to next vassal's demesne. Even then, the bonus is not big, so not sure it would make significant difference.
War for Arabian Empire mostly took place in the Nile Delta.
I wish Nile was navigable like in history.
Caliphate is doing a lot better than expected.
Also so hard to see with two Caliphs, Jain emperor, and assorted minors all being green.