You most likely consented to future changes to the ToS. It's kind of like their version of asking a Genie for infinite wishes as one of their three wishes.
I'd like someone to address this. Surely there's a limit. The statement "your account balance belongs to Twitter" is not against the law (like they can say the service is worth whatever amount of money and that you owe them this money), but you're not allowed to do that, because you're not allowed to retroactively change a contract's terms.
So, surely, you can't change ToS retroactively and expect that any of it applies?
Let's breakdown what tos is. It's the terms they are enforcing to provide you a service. They can refuse you service at any point for any reason. You can have your own terms of service that they must follow or you will refuse to do business with them.
By adding that they can train AI they are trying to get out of a future lawsuit that may happen if the courts require consent for training (current anyone can train on anything).
Your right to sue them for using the data they hold might be lost if you continue to use after the term change.
If they asked for your car and you refused they could stop service but they can't take your car.
They can't change payment terms from the past and sue for them. But if they change the tos to say it costs more now your next bill will go up. If they say they can use your data now that they hold and you have an active account they could take that as an acceptance that past/future can be used to train ai.
A better example might be a right given. For a year you could download photos for AI training. Today they forbid that for all future and past posted photos. Anything downloaded before the date can be legally used to train.