I don't know what the law says about this, but "for no reason" is always different than "for any reason". Because you sued them is a specific reason, that they might be prohibited from retaliating based on (or might not, again I don't know).
The classic example of this is race. You can not hire someone, or deny someone service, for no reason. You can't however not hire them, or deny them service, for the reason that they are black.
"I <did x>, and then they took the rare action of closing my account (which they're not allowed to do in response to <x>) for no apparent reason" is more than enough to
1. Get discovery to gather further evidence
2. In the absence of a convincing rebuttal from Google ("he was sharing copyrighted movies via Google Drive, and per our policies we closed his account like we closed 1000 other peoples accounts. Our policy is exhibit A, the list of copyrighted movies he shared is exhibit B, the list of other similar accounts is exhibit C"), is probably enough to win a civil court case by itself.
The standard for civil cases is generally "on the balance of probabilities", not beyond a reasonable doubt like in criminal cases. Courts are allowed to rule on what seems like the likely reason that someone did something.
Disclaimer: Not a lawyer, bladdy blah blah, if you take this as legal advice your both a fool for not consulting a lawyer, and taking advice from someone on a topic where they themselves admitted that they don't know if Google is even prohibited from doing business with you in this hypothetical.
"Additionally, we are electing to terminate your Cash App account (as allowed in our Terms of Service, section XIII.8). As a result of the termination of your Cash App account, you will no longer be able to use Cash App and its services going forward."
XIII.8. Termination of Account
We can terminate or deny you access to our services at any time, for any reason. You can also choose to deactivate your account at any time.
We may terminate these Cash App Terms or any Terms, or suspend or terminate your Account or your access to any Service, at any time for any reason, including a violation of the Terms. We may add or remove, suspend, stop, delete, discontinue or impose conditions on Services or any feature or aspect of a Service. We will take reasonable steps to notify you of termination or these other types of Service changes by email or at the next time you attempt to access your Account. You may also terminate the Cash App Terms applicable to your Account by deactivating your Account at any time.
The classic example of this is race. You can not hire someone, or deny someone service, for no reason. You can't however not hire them, or deny them service, for the reason that they are black.