Some measurements of the dark streak imaged on October 22, 2020 on Mars. And some interesting findings...

First, using Winjupos, two maps were generated, and the streak’s length was measured at over 600 km. Interestingly, 
on the Mars Orbiter Map, there are no features that could be accounted for such a dark aspect. 
Position for 22:19 U.T.: Eastern end: L1=128.5 B=-10.6 , Western end: L1=137.4 B=-5.8.

Secondly, the dark streak looks that it shifts its position and also fades as it gets further away from the terminator. 
It actually looks like it is moving with the surrounding clouds (which are visible in the animation in comments).


More on the dark streak, this time with data from two days. It shows aspect changes in almost 24 hours in the red filter.

[Maximilian Teodorescu:Dumitrana,Romania]