Nope, but they can lock after launch using data from the jet's radar or helmet cued targeting. Pretty much an "It's over there somewhere. Kill anything you can see in that location/velocity." Then the sidewinder points it's sensor where the jet tells it to and uses UV/IR to find it.

The 9x is to the original sidewinder what your smart phone is to an abacus. Shooting down balloons with it is pretty wild. Even if they don't have the proxy fuses or warheads.

No laser designation needed. Aim-9x have full infrared and UV imagers in the seeker head. A white balloon in the sun floating in cold air at 60,000 feet might as well be a lighthouse