It comes down to something simple.
The Germans were planning to cross in canal barges, many of which were not even motorized.
The British were planning to attack said barges with a mix of destroyers, cruisers and battleships. The Germans had no way to stop this. Their navy was too small. The Luftwaffe could only operate during the day, and could inflict casualties on the Royal Navy, but not stop it.
If the Germans had tried it would have been a massacre. Which would have been a great thing.
Yachting, the only sport where you get to be a mechanic, electrician, plumber and carpenter
I served in the US NAVY amphibious forces in the 1960s. The task of moving men and material from the sea to shore against resistance requires specialized training, skills, experience and equipment. I do not believe that t he Germans had prepared for an amphibious assault early enough and n any case probably did not have adequate landing craft, etc. available. I may be wrong though not having made a study of that period.
I think I have somewhere a book by C.S. Forester (Hornblower etc...) with short stories, one of which tries to describe how well (or not...) the German invasion force would have fared.
The US suffered a significant loss of life - nearly 1,000 dead in one incident, which was covered up for some time, during training for the invasion of Normandy.
https://en.wikipedia.org/wiki/Exercise_Tiger