The answer is within the question.
24MP , 20.2MP and 36.4 MP are numbers that define the resolution.
They all have the same sensor dimensions but one have more pixels along the edge than the other.
Those who have less resolution has bigger sensor cells which captivate more light and as such are, theoretically, better in low light photography.
Pini
I was looking thru June issue of Pop Photo and found this ad from Adorama
Leica Q Full-frame 24MP CMOS Sensor $4250.
Canon EOS_1DX Mark II 20.2 Megapixel full-frame CMOS sensor $5999.
Pentax K-1 36.4 effective MP (full sensor) $1799
So which camera has more resolution as they all have full frame (35mm) sensors?