You can move the data/game to another drive using the STEAM interface where you initially install the game.

Goto the Library.
Highlight the GAME you wish to move.
Right mouse click on the Game.
Select Properties.
Click on installed files.
On the right side of the Installed Files window,
Click on the "Move istall folder' button.
Select the new drive/folder for the Game.
You may have to select the new drive using a drop down menu.

That doesnt always move the mod folder though. Just the game. Some mods download to game folder I think. others default to OS drive I believe.

Originally posted by dragonsphotoworks:

That doesnt always move the mod folder though. Just the game. Some mods download to game folder I think. others default to OS drive I believe.

Unless you are using a mod manager such as VORTEX, the mods will move with the respective game. Vortex has its own area for mod storage.
For example:
Vortex default folder: {USERDATA}\{GAME}\mods
Translation: C:\Users\me\AppData\Roaming\Vortex\horizonzerodawn\mods
So if the original poster, (The Unity Beast), is using vortex, he would have to move the program to a secondary drive. Me, I just switched all my drives to 2TB SSD's. end of storage issue.

I gave up and got a 4 and 6 terabyte drive. Got tired of running out of space on drives and on PS5. So got a 6TB M.2 for PS5 and a 4TB for PC. Wasnt over priced when I got mine though. Not sure price on them now.