Similarly, you may ask, can you get mods for Subnautica?
Installing Mods
These are graphical mods which need to be installed directly to the game folder and require the Reshade application to be installed. Some mods such as Nitrox (a multiplayer mod for Subnautica) use an executable (EXE) or Windows Installer (MSI) files which cannot be installed via Vortex.
Also, is modding steam games illegal? Mods aren't illegal, as far as I know. Steam is only a game distribution vendor, like it's been mentioned here already. You purchase games through it, play with through it, and that's it. Gamers of Skyrim, Fallout, and others, are known for being heavy modders as well.
Also to know is, can any game be modded?
The game itself has to be moddable first (either by design, or work around is feasible). Some developers don't take mods into consideration while making the game and some make it almost impossible to mod only because then they can sell every possible free mod as a paid DLC or new game (I'm looking at you Hardline).
Is Nexusmods safe?
Nexus is completely safe. I recommend a 'sprint mod' so you can move faster when in the middle of nowhere. I also recommend a 'perk every level mod, that lets you relax and buy weird perks that you otherwise wouldn't ever end up getting. You don't need the perk mod every Playthrough but it gives you options.