Grindr wouldn’t be the only way to declare one’s STD status though. It could be omitted from one’s profile, but declared during chat, for example, or prior to hooking up.

Methinks you don't understand the problem space. Putting it in your profile is intended to save the afflicted from wasting tons of time and energy on a. talking with people who will immediately nope out when they learn your status and b. dealing with a lot of emotional BS from people who want to see themselves as nice but who aren't really ready to deal with you and your situation.

That can be a hard enough conversation to have even if they know. Being straight up rejected by some high percentage of people who started to chat you up and are done the minute you mention HIV would be a dreadful experience. It's possible they are on the app precisely for the ability to pre-screen people for their willingness to hook up with someone HIV positive.

Given the current reality, you can do either of the following here:

A) Mark yourself as HIV positive in your profile, which Grindr will share with third parties.

B) Directly declare yourself as HIV-positive at some point in a conversation.

I’m not suggesting there are options without drawbacks.

I imagine a lot of folks declared it in their profile without knowing it would be shared and they probably declared to try to have a more positive experience over having one dreaded discussion after another. I think those folks have reason to be upset.

I agree that they have every right to be upset. Grindr didn’t need to share that kind of information with third parties.

Illegal how?

Presumably illegal in the sense of https://en.wikipedia.org/wiki/Criminal_transmission_of_HIV (and note that in some jurisdictions "exposure", not just "transmission" is criminalized, per that wikipedia article).

Except you can decide if you want HIV status to be displayed and the last time I mucked with my profile, it was optional anyhow.

Its not even clear if whats being sent to the analytical companies is whats displayed in the profile or all fields even if they are not displayed.

I believe in certain places that if you withhold the information of being HIV positive from someone you have sex with and infect them, it's a pretty serious crime. I think it might even be a crime if you don't infect them.

Depends on the state. The majority of states either have laws relating to disclosing known STDs or laws specifically about disclosing known HIV status, or both.