How to recreate these effects I found on IG?
You need a video editor that let you add curves to your video. Davinci Resolve is a great option.


Convert it to grayscale, you can simply reduce the saturation to 0.
Invert the curve. Augment the contrast making the curve more vertical.





Bring the green and Blue channels all the way down




Play a bit more. But that is the idea.





Option two for the final color is to add a color rectangle with different blending mode in the editor.



https://pixabay.com/es/photos/verano-flor-cabello-retrato-cara-4246927/