In mods map i think.

If it shows up in game it should be uploadsble.

I thought so but it doesn't show up ingame...
It only shows up if I put it in "assets/builtin-mods". And from that location, it doesn't allow me to upload it to the workshop.

Have you made a folder with a tumbnail and propertie file?

Yes I did. Doesn't work (while I've strictly copied how other maps do!).

Btw even when I select the map ingame (through Skirmish when put in skirmish folder, or Custom/Sandbox when put in mods-maps folder), it doesn't read the map's picture...

Have you tried to put it in Units?

Okay I just tried, and it works when put in Units...
Phew. It's a bit absurd but at least it works. Thank you!
Now I need to find out how to make that ingame thumbnail work...

Thumbnail working now. I guess it was either too big, or something had to be named differently.

Yeah sorry it is absurd at putting it in units, but that's best way to do map upload to the workshop. The units folder is basically a mods folder now, I need to fix the naming somehow without breaking everyone's old setup.