Incidentally, it's about the same length as this 3 mile path, 4.2 km.
This path looks more like the rights of way over Morecambe bay though.
In 1909, they sent them up the Pyrenées mountains to be attacked by bears.
From https://en.wikipedia.org/wiki/Mont-Saint-Michel: “converted into a raised causeway in 1879“
We went by, on holiday, a few weeks ago and the authorities simply crammed the entire place full of tourists. It felt like a BLM protest without angry people: every square meter had at least 5 people on it. Corona? Haha! Tourism income please. We ran away minutes after arriving.
Coming from NL, where authorities allowing that kind of madness would be front page news, this really baffled me. It seems that the French think that as long as you wear a face mask, nothing else matters.
I had just blindly assumed that the local authorities would limit parking (it's in the middle of nowhere, pretty much unreachable except by bus or car), or do some sort of reservation system, so tourist counts would be limited and people could keep their distance. Instead, the only sign of government presence were the four heavily armed police officers at the entrance, and they didn't give a damn either.
That said, just like looking at Paris from atop the Eiffel tower is a bad look because, well, no Eiffel tower, the Mont-Saint-Michel is best enjoyed from a distance. So maybe we didn't really miss anything except an overpriced crêpe-au-chocolat.