“I don’t know how they are going to enforce the 100k rule”
As you probably know there is an EUR 10K rule for moving between EU/UK countries. While difficult to enforce, you must declare the cash over that limit by law.
So the objective is really to allow the authorities to make you a criminal if you fail to do the declaration. Once you have that criminal record you are really under the thumb.
They have a rule like that in America. There are many well documented cases of people on legitimate business having their money seized by the government then having to fight to get it back, or sometimes never getting it back at all.
This new rule is that you aren't allowed to have 100k in cash, period. Even if you stuff it into your mattress.