If when your FPV drone is wobbly when descending horizontally, then it’s a sign of low throttle instability and you can try my suggestions here to attempt to fix it.
Try these suggestions one by one. Each time do a punch out, then lower throttle and let it fall horizontally (with the quad levelled to the ground) and see if you get any wobbles.
Motor Idle Throttle Value
Raise the Motor Idle Throttle Value as high as acceptable for you. Default is 5.5% which might be a bit low for low power rigs.
This might be the easiest “fix”, the downside however, is the reduced “hang time” when doing inverted moves, and the drone doesn’t come down as fast as you might want when you drop the throttle. Also it reduces throttle range, if that’s something you don’t want, you can try other methods instead.
Turning Off D_Min
D_Min is the minimum value of D gain when the quad is in a stable position, D gain will only be raised to its normal value when the quad is rotating for example when you are doing a sharp turn or doing a flip,
A higher D gain will help minimize overshoot and bounce back when the quad is rotating rapidly, but by using D_Min and trying to keep D gain as low as possible during flight will help motor cooling and excessive vibrations. But Having D_Min can sometimes cause instability when the quad is in a stable position.
The downside of disabling D_Min is the risk of motor overheat, so that’s something to look out for when you do so, make sure the motors are still cool after turning D_Min off before proceeding.
As mentioned above, higher D gain helps improve stability, therefore, by raising D gain (or increase PD Balance slider to 1.1 or even 1.2) might help with instability. But again, high D gain might cause hotter motors, so you want to make sure the motors are not getting too warm after the adjustment.
PWM Frequency in BLHeli
If nothing helps, try this as a last resort. Lower PWM Frequency in BLHeli, for example, from 48KHz to 24Kzh, from 96KHz to 48KHz etc. The default is 24KHz and that’s the lowest I recommend running. Your motors run smoother with higher PWM Frequency but it reduces the torque, and so it could be the reason that causes instability at low throttle on your quad.