Takwis Re your remark about fresh paint - good observation ;-) it was freshly painted aircraft indeed ... was an Ethiopian MAX delivery flight.
737 Driver the image you posted has only one of the smaller strakes ... so when was the second strake introduced ... my guess based on Takwis answer and PEI's post is the -600 to -900 ... so you would expect a reason for that... do you know what 737-model that KLM plane was?
737 Driver in the image that I posted I indicated the difference between the 'trapdoor' and the 'leading edge' ...IIRC the trapdoor opens down and forward and is as far as I could see not a part of the moveable leading edge/slats ... it would require a detailed picture of a MAX to clear that up I guess (would be nice to see one),
PEI_3721 could it still be that these 2 strakes have both a mechanical and an aerodynamic function ? ... it appears that there where enough aerodynamic issues to solve, even going from Classic to NG and on to MAX, so you could expect some changes in these area's ... like difference in size and position of the big strake (it looked increased in size on the images that I had) ...