So the root of my "water tank empty please refill" problem with my Dreame robovacume was that the magnet float in the tank that indicates empty or low water level had filled up with water. Permanently sinking it to the bottom and indikating empty. Easy fix; empty the float of water. Such a dumb design.
Anyway it can now use the mop again. So that's good. Now I can feel better about beeing super lazy about mopping again.