No. Not your health information, not your medications, not your Room Check, not your messages, not your notes.
And this is worth understanding properly, because the reason matters more than the answer.
It is not a setting you have to trust
A sponsor is not a member of your Circle. They cannot be added to it. So there is no privacy switch protecting you from them, because there is nothing on the other side of a switch to turn off.
That is a stronger promise than a setting. Settings can be changed by accident; a person who is not in the group cannot see the group's information at all.
What a sponsor does see
One thing: that you accepted their gift. That is the whole of it.
They do not see whether you use SeniorThrive or how often, and they do not see your check-ins, whether you slept badly, or what you talked to your companion about.
Who sponsors are
Usually a financial advisor, sometimes another professional, who covers SeniorThrive for the families they work with. It is a real arrangement and a generous one, and it comes with no strings into your account.
If the sponsorship ends
Your account does not close and your information is not handed anywhere. You move to the Free plan, which never expires, and you can take over the payment yourself if you want the paid features back.
Nothing you recorded is lost in the change.