How to open the lid of this toilet water tank?
The solution was similar to one of the ways Michael Karas suggested in his accepted answer. I used a pliers wrench to grap the outer ring around the flush knobs and turn it counter clockwise. I used considerable force, risking that I would break some of the plastic parts. This was the solution.

I managed to open the lid this way and found something similar to Michael's second picture. Turning the ring should have unscrewed it near the top, but it got unlocked near the bottom instead. (I plan to add pictures.)