This range fan drips water
More than 20 feet of flex pipe is a problem - 20 feet of flex pipe, uninsulated, sloped so it drains back into the fan is a huge problem.

Flex pipe has VERY high resistance to airflow compared with smooth duct. It should be avoided, or if its absolutely unavoidable it should only be used for very short sections where regular fittings will not work. I don't recall for sure but I believe that the stuff is normally forbidden on a range vent since it cannot be cleaned very well, and grease buildup is an issue. If the "flex pipe" in question is dryer vent hose it's VERY not suitable for range hood venting.

Long duct runs from fans venting moisture should be avoided, and if they cannot be avoided, the duct should turn to slope consistently towards the exit as soon as possible so that condensate runs out the exhaust. You may also need to increase the size of the duct to lower resistance.

Ducts carrying moisture should be insulated to reduce the condensation of moisture inside the duct.

Sure, you can slap a bigger fan on, but without solving the rest of your issues it may not help much.