Another term to search for is “centrifugal fan” - these are the type used where air flow restrictions are significant, as they can compress the air some unlike a traditional box fan.

Where’s the return on your air handler? If there’s more than one (one upstairs, one down), you may be able to cheat the system by blocking one seasonally.

Also most likely the air handler speed is set too high - installers are kind of lazy (they don’t want callbacks) so they typically set the air handler to max speed. Since most instalsl are also well oversized, this means the system will short cycle and move less air during that short cycle. Lowering the air handler speed may help lengthen the cycle, moving more air in total.

You could also try just turning the air handler on (fan mode orn"Always On" on thermostat).

This probably won’t solve your problem entirely, just maybe help.