Elder Scrolls series forum Install SkyUI, which has a Mod Configuration Menu (MCM) as a feature. And note that you'll need to use Vortex from Nexus Mods to install and manage mods.

I do not use Vortex so I will not be using this game.

Thank you for your reply.

Or MO2 when they add support for it... or Wrye Bash, which is what I've always used.

You don't have to use Vortex, you can even mod manually. The main issue so far is that Skyrim GOG uses different paths and that haven't been updated in other managers.

MO2 and Wrye Bash (and also LOOT) have received an issue ticket on Github so it shouldn't take too long. That includes NMM. Just wait a little (as always with any updates) and let it take its course. Remember, the Vortex team already had ample time to change Vortex at the time GOG released Skyrim...

So, until then you have to create plugin.txt file and manually add the mods. Or, use a mod manager to install a mod and then copy the files to %localappdata%\Skyrim Special Edition GOG. Might not work with every mod, though.

I can't stand Vortex (reminds me to much of the unintuitive and chaotic Metro UI) myself so I'm going to wait a bit either way.