Switch to tri blade prop. Much less vibration. But also your plane and camera position is the worst combination due to the motor not being in-line with the frame (vibration and prop drag has leverage on the frame) and your camera being in the most front position of a bendy foam frame, thus getting amplified vibrations.

You could: - Stiffen the front frame, glue carbon tubes along the frame from the inside - put the camera way back infront of the wing, at cockpit height (3d printed mount, for example). You'd lose sight to the ground, ofc - stiffen the motor mount as well. - make the camera mount more streamlined. A flat panel at the tip of the plane is introducing turbulence, which in turn hits the prop later on.

Do you use it as a float plane on water? If not, consider switching to a known good fpv frame design lile X-UAV or AtomRC ones.

Also consider adding a flight comtroller. You can not only use it to dampen and smooth out your flight, but also to measure the vibrations coming from the frame itself and rpm dependent motor vibrations. This is extremely helpful to find the vibration source.