For 2d sprite games, OMG yes, you could provide some very accurate motion vectors to the encoder. For 3d rendered games, I'm not so sure. The rendering engine has (or could have) motion vectors for the 3d objects, but you'd have to translate them to the 2d world the encoder works in; I don't know if it's reasonable to do that ... or if it would help the encoder enough to justify.

Schemes like DLSS already do provide 2D motion vectors, it's not necessarily a crazy ask.