This is not an ex post facto law - the question is purely "are the terms of your contract enforceable?". For example I can make a contract that has a term "all

This is not an ex post facto law - the question is purely "are the terms of your contract enforceable?". For example I can make a contract that has a term "all people of gender/race/age X must be paid no more that 50% of the amount paid to people of gender/race/age Y", but if I were to then sue a person that agreed to this contract they would immediately be able to say "that term is not enforceable". The FTC ruling on non-competes is no different - no one is saying "a non-compete clause breaks the law in a way that would allow criminal or civil suits", they are saying "this clause is not enforceable" (plenty of standard contract terms are not enforceable depending on state and/or country, and the unenforceable nature of the term does not - for better or worse - invalidate the entire contract).