I am trying to reach out for the one who made the "Ingress Mission Day Missions" in MyMap. It's very well made but the filtering / use of layers can easily be improved. Can you reach out to me if you are the owner?
It's @NianticBrian, and I assume the reason the layers are not organized is because Niantic ran a script through their database just to get the missions on the map. You should be able to make a copy and customize it to your liking however.
I kinda guess someone made a script for generating it but you confirmed it. I have tried to copy the map but it probably has too many items for it. Get a 502-error.
edit: I tried exporting as a KMZ-file but got an error due to size limitations when i tried to copy it into a mew map.
edit2: managed to copy it but not sure if i should have one layer per country or one layer per continent. Problaby have to sleep on it to tomorrow.
You can alse use https://bannergress.com/map?onlyOfficial=1 to see all the official mission collections by Niantic that are valid for the upcoming second sunday mission days. (You need to zoom in to see all in an area, not all are shown when zoomed out)