Canon SX620 HS has a 20.0MP 1/2.3" (6.17 x 4.55 mm) ) sized BSI-CMOS sensor and features DIGIC 4+ processor. On the other hand, Sony A7 IV has a 33.0MP Full frame (35.8 x 23.8 mm ) sized BSI-CMOS sensor and features Bionz XR processor.
Sony A7 IV's sensor provides 13MP more than Canon SX620 HS'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.
One other difference between these two cameras that is worth mentioning is that Sony A7 IV's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the SX620 HS and A7 IV sensor size comparison.
As seen above, Sony A7 IV has a 30.4x Larger sensor area than Canon SX620 HS. 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.