Nexus Mod Manager has been dead since gosh, 2017 or so I want to say. They kept it around for a few years and I think you can still get it from somewhere on their site but iirc they hired the guy who made Mod Organizer 1 to make Vortex, the new Nexus Mod Manager. Mod Organizer is amazing though so idk why Vortex sucks so much.