!!!Please note that there seems to be a bug in version 1.11 of the game, that can delete all your unlocks and bonus money.
If you quit your game after finishing a campaign and later come back to the game, the save can be empty.
I managed to work around this bug, by immediatley starting a new campaign from the save file after finishing a run. Do not quit the game before your newly selected fleet is back started in the city of Ur.!!!

This guide contains spoilers, so if you have not reached the endgame, be aware.
Following this, you can unlock the heavy cruiser Varyag to select as your flagship in future campaigns in this save slot. It is the meanest stock combat ship out there and can obliterate multiple strikeforces (just don't try to repair it in one go).
First of all, I do not know if this is the only way to unlock it, but this is the way I managed it.

To unlock specific dialog options in events, I think you need a high worldview "Faith". Try to select religious and mystic options as much as possible during events, and try to avoid talking down on faith during Tarkhan recruitment.

At one point when landing in a new city, you are asked to visit an old doyen.
Accept the invitation and when asked why you can read the holy texts, claim it to be a miracle.

When the darkness comes in an event, always choose the faith options and adress your soldiers as "Brothers and sisters..."

After some time, in your next speech to the fleet, again choose faith ("All of this was meant to happen...") and claim to be the prophet.

Finally you will be asked by the Lord Governor of Khiva to meet him alone in the valley of Basra.
If you meet him in a single ship (park the fleet a few km out in the desert) and talk to him peacefully, you should now have the option unlocked to once more claim to be the prophet.
Now you can try to recruit him in the recruitment minigame.

If you succeed the Lord Governor will join you, and you now have the Varyag unlocked for future campaigns, congrats!

See https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2576791911 for details on the minigame.
The worldview of the Lord Governor:

• Romani
  Always Positive
  
  
• Gerat
  Random (tending towards Negative)
  
  
• Kindness
  Always Positive
  
  
• Force
  Random
  
  
• Wealth
  Always Negative
  
  
• Fear
  Random
  
  
• Order
  Always Positive
  
  
• Faith
  Always Positive

• write down the specific event choices
  
• find out if there is another worldview to get the Lord Governor to join