my Game Isnt Letting Me Select It Because Missing Descriptor File

This is something that comes up with Paradox games regularly, unfortunately. First, check to see if you have the descriptor file in the appropriate folder. For this mod, the file is called ugc_699709023 and should be located in the folder C/Users/(Your User Account Name)/Documents/Paradox Interactive/Hearts of Iron IV/mod. Delete that specific file, then unsubscribe and resubscribe to the mod in the workshop. Once everything is finished downloading and unpacking (this will probably take a few minutes, don't rush it) run the Hearts of Iron IV launcher through Steam and give everything a couple more minutes to validate. This should generate a fresh copy of the mod descriptor file.

tl;dr delete the descriptor file, resubscribe to the mod.