Yes, it was api & driver level iirc (you adjusted the "difference between the eyes"/two different fov points), basically anything polygonal 3D worked I think.

But your PC also needed to produce twice the fps (for each eye a separate set ... so if your monitor could do 120Hz (I had a Samsung 959NF) & your card could do 120fps you got 60 frames per eye), ... so there was a limited number of games that had a playable fps even with a top pc (with home-made water loop!).
And this is "3D effect within the physical monitor" (unlike VR goggles that fake the 3D perception from close to your eyeballs) & most games dont really have 3D objects displayed close to you, eg in fps like Quake 2 the gun was noticeably 3D, but the rest (correctly) much less simply bcs of the fov/the distance.

Also CRTs weren't extremely bright & the glasses (with the LCDs "open") were still kinda dim so it was like playing with uncomfortable sunglasses.

Fun as a gimmick, still remember it fondly.