I embarked a Horseman unit from my Harbour while there units from other empires nearby. My cursor became locked with a preview of the battle odds on the screen. I could pan around, click on notifications, but could not click on cities, units, or open up any menus, including the game options menu to save and leave normally. Had to alt+tab out and close.

I had the same problem while trying to hunt some wildlife.  I would see a battle preview on the map, but it would not let me start/ignore the battle.  I could see the deer that it was trying to start the battle against, but it was sort of semi-transparent like the game was greying it out.  In addition, it would not let me move my units unless I explicitly clicked the move icon on the right-hand panel, but that was even difficult because the panel would often deactivate before I could move my cursor to it.  I was able to resolve it by saving my game, closing Humankind, starting Humankind again, and then reloading my save.