I saw videos with this mode in the game, but I don't see it in the latest version. Was it only in the experimental version previously?

Update to Post for sake of not making another topic, this version really seems to work my GPU hard. capping at over 90% usage inside the base. Nothing seems to reduce this aside from turning off the shadows which obviously, I do not want. Does anyone have any suggestions? The temperature isn't going into dangerous levels, but I'd still like to reduce the load since its impacting CPU heat as well.

No. You might have to get to a certain point of story mode to unlock it, similar to Endless and Sandbox.

Huh, you might need the event first (like how you need the demo complete achievement to unlock sandbox)? wait a few days (it happens on the IRL 24th of each month so you're in luck) and play until it happens, or setting your computer time to the 24th manually should work

supposedly it can also happen extremely rarely totally randomly but you probably don't want that if you're just wanting to try the gamemode lol

Maybe I do need the achievement, would make sense. Oh well, time to prepare in a new save.