That depends on your definition of "work". The GPU your monitors are plugged into is going to be your renderer, while the other won't do anything
So if "work" means that you'll get a display, it'll work. If you were expecting them to work together in some way, I'll have to disappoint you. The thing you might be thinking of here, SLI, is no longer supported on modern GPUs and has been... opportunistic at best in the past
#So if i got a 4090 and 3070 and just put them both into the motherboard would it work?
autumn umbra
bitter moth
You can use them both for compute purposes if you're into that, though most modern uses (ai) prefer more vram than the 3070 has
or if you're feeling particularly silly, use one as a dedicated physx card in the handful of nearly decade old games that support hardware physx just to flex
once the novelty wears off though, you'd be much better off selling it or re-using it in a side pc