From the contact us page on their website?

https://support.signal.org/hc/en-us/requests/new

@signal There remains a question of what happens if the group chat membership changes between when the poll is sent and when the response is sent. Presumably the response is sent to and can be decrypted by members as of when the response goes out. What does a new member, who missed the poll message, see?

@david42
That's right. Everyone in the group where the poll is run has complete access to the poll results.
@signal

@david42 @signal yes

Not sure if this is what you're looking for, but support@signal.org has worked for me in the past.