Ha, Ha, Ha, how little you know. Want to trade onion futures? Well you can't because onion futures are illegal. The Onion Futures Act making onion futures illegal was passed on August 28, 1958 and is still the law.
Well, I meant trading in general, in other words Nebraska can't prohibit futures and options trading..... But I learned something new about onions today... Kosuga was pretty sneaky. He reminds me of Jesse Livermore. https://en.wikipedia.org/wiki/Vincent_Kosuga
Also, CFDs are banned for American residents. There are many bans and restrictions on all kinds of financial instruments all over the world.
A state generally can't regulate something involving interstate commerce that is already federally regulated. You won't find any examples of a state banning interstate tulip trading if federal law allows it, for example.
The ban on forex trading in Ohio and Arizona in the fine print in black and white at the bottom of this page: https://www.tdameritrade.com/investment-products/forex-trading.page Unbelievable.
I don't think "ban" is the word you're looking for. The link you provided indicates that TOS doesn't accept forex customers from Ohio and Arizona, not that forex trading is in any way banned in those states. Most probably there is a compliance or registration requirement in those states that they don't find it economical to comply with given the amount of profit they get from forex in those states, so it makes business sense for them to just not accept forex customers from those states.