Panasonic FZ80 has a 18.0MP 1/2.3 (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Venus Engine processor. On the other hand, Sony A6400 has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz X processor.
Sony A6400's sensor provides 6MP more than Panasonic FZ80's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the FZ80 and A6400 sensor size comparison.
As seen above, Sony A6400 has a 13.1x Larger sensor area than Panasonic FZ80. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.