How do you make a .mod file? I think one time I did it using the paradox launcher but idk how to

You can create the .mod file, along with the folder for your mod, by going to "All installed mods" in the launcher:

Then pressing "Upload mod"

And then in the popup that appears, press "Create mod"

Then fill in the details in the popup which would be correct for your mod (the name, what tags it should have, and which folder it should be saved to)

Press "Create mod" and then a new folder should be created in "My Documents/Pardox Interactive/Hearts of Iron IV/[whatever value was in the "location" section]" - so for me, using the above "My Documents/Pardox Interactive/Hearts of Iron IV/mod/example".

Thank you!