How do I opt out of a group text message sent to me
Ask the sender to remove you from the group. This is not a carrier function.
Unfortunately you cannot opt out. Anyone responding to the original message will continue to send the response to you along with everyone else in the group.
The only way to opt out is to never have been in the group to begin with.
You can request to the originator of the message to omit your name from the group for any future group messages. Of course they can either honor or not honor your request.
I usually block the original sender for a few hours. By then most of the replies have stopped. I then unblock them. Feature depends on app or phone used.