> or that claim things that are per se considered damaging --- a specific and limited list

Standard disclaimer that law varies by jurisdiction. However, that limited list typically includes claims that the person committed a crime. Many juristictions also include accusing someone of having a contagious disease, engaging in sexual misconduct, or engaging is misconduct that is inconsistent with proper conduct in their profession.

In other words, the types of things I would expect people to be talking about on tea overlap heavily with defamation per-se.

If the users were careful to make all of their statements opinions, that defense would work. However, I doubt that is the case. Instead, I expect many users to include example of what their ex did that led to their opinion; which gets directly into the realm of factual statements.

The provider protections are real, and likely protect the app from direct lawsuits (or, at least from losing them), but do not protect the app's users. A few news stories about an abusive ex going after their former partner based on what they posted in the app could be enough to scare users away. You don't even need to win the lawsuit if your goal is to harass the other person.

It does, but those bars to defamation claims are based on the US Constitution more than they are on state law. I think another way to put that is that I gave the maximally generous interpretation to the plaintiff there.

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