On vintage/mechanical machines, sometimes you can rig something that will mechanically raise and lower the foot lift bar, but it takes quite a bit of fabrication to do so (a lot of older commercial machines have the mechanism on the outside of the machines that does just that).
Most modern / electronic machines it would need to be part of the machine to start with.
I love having a knee lift for the foot - it's so nice to have both hands free to get the fabric in just the right spot while lowering the foot in place.