iMessage on MacOS broken after iOS and iPadOS 26.1 update

I opened iMessage on MacBook Pro (M1, macos 15.7.2) after iOS 26.1 update to iPhone 11 Pro and iPad Pro (3rd-generation). In a message thread with 4 other people that I used to be able to participate in across MBP, iPhone, and iPad, there is now no entry field to participate in the message thread. I can see updated messages, but there is no place for me to type a reply or start a new message to the group. I can respond from my iPad and my response appears in iMessage on the MBP, but I can't enter text on the MBP.