@AbuHajaar
OMG, because of your comment, I rechecked the chapter...
The author actually only does line work and screentones.
Every shading is done by screentone...
Either this mangaka has and army of assistants or it's done digitally.
Seeing the artifacting and the clones everywhere, pretty sure this was drawn on a computer, with a lot of copy/paste...
Here some clones in this chapter alone:
@Acolytus
Pretty much take a photo, desaturate, color dodge and gaussian blur...
Here's an example tutorial.
https://youtu.be/AesJUS2yO2c
And I'm pretty sure the background characters where either from stock drawing or the author prepared a selection of them to copy/paste everywhere...