I can sneeze and before I finish, I can make a throwaway account for nexus and start downloading a terabyte of mods via Vortex.

Umm... You can download mods manually without the need for having an account. You don't have to log in or anything. It's just a place where mods are gathered together. It's not like the Creation Club at all. Sure, if you download the mods manually you have to keep track of every added mod by yourself (just like in those early days where you had to work without any mod organizer).

Sure - If you want a convenient way of installing mods, you can opt for a mod organizer (Vortex), and then you need an account. However - You only deed it at the mod deployment stage. After that you can close down the program and you can play Skyrim without any need for a client running in the background (like with Steam and the Creation Club).

In short - Using Nexus and the Vortex mod organizer has NOTHING to do with DRM. It's just a tool that you can (but are not forced to at all) use at the mod deployment stage. After that there is no need to for it to play the game.

I don't think that is correct. You must be logged in to download files from Nexusmods, also for manual downloading. If I remember correctly, I could do so when I visited the site for the first time, at least mods with a small file size. But that is a VERY long time ago and no longer possible. Maybe they handle this differently depending on your country for legal reasons, but I never used my VPN for Nexusmods, so I can't tell for sure.

Yes, you must be logged into an account to download files from Nexusmods.
No you do not need Vortex or any other mod manager to use mods.
All files can be downloaded manually. Only some can be "Downloaded with Mod Manager" and that depends on the uploader. I know, I am an author of a few simple mods on Nexusmods.

Manually installing mods can be technically challenging (easy to brick your game) that's why many people use mod managers.

Alright - I stand corrected then. I am a long time user of Nexus, so I presumed that downloading goes without being logged in.

However - I still don't see that as DRM, like some people seem to suggest. You use Nexus as a place where mods are neatly organized, and you can use a free mod organizer (Vortex) that will download and install mods hassle free. But you are not bound to Nexus or Vortex. The game will run even if you never visit Nexus. The game will run if you never use Vortex. Both are not mandatory to run the game, so they cannot considered a part of a DRM system. Period.

How do you manually enable/disable mods that you have installed? I can't seem to get a straight answer for this.

Use a * in plugins.txt to activate them, and remove it to disable them.

%localappdata%\Skyrim Special Edition GOG\plugins.txt. Create it if it's not there.

Example:

*Unofficial Skyrim Special Edition Patch.esp
*SkyUI_SE.esp
*iHUD.esp
*DDLevel20.esp
*SkyrimTogether.esp

EDIT:
Alternatively, if you use MO2 right now, just copy plugins.txt and loadorder.txt to the folder above. Or, use symlink.

Personally I don't like the politics of the people who run the site, as long as the mod isn't adding pedophilic content or being used to cheat in multiplayer games I think you should be able to do whatever you like. That said, nothing stops anyone from making a throwaway account and keep the mods backed up on an external SSD or usb drive.

It hasn't been like that for quite some time. You need an account to access the download page, even if you click manual download the bottom of the page will say you need to log in to download the file.

MO2 has since been updated to support the GOG version.

Right, I've followed along on GitHub. But thanks anyway. :)