Messages app opens in last conversation rather than conversation list

Well, I would prefer that it open to the conversation I was having rather than going back to the list, unless I had closed that conversation. In other words, I want it to remember the last state I left it in, which is what it does. It may be a simple fix to you, but it would break the app function for me.

And Apple won’t see your post in this user-to-user forum so there’s no point in asking them here to change the behavior that has worked the same way for 14 1/2 years. If you really want Apple to change it the place to ask is https://apple.com/feedback, and if they get thousands more requests for the same thing they may change it. In which case I would have to go and complain that they broke it.

The Messages app will retain its closed state. In other words, as you described, you closed Messages from a Message, not from the Messages list. Dealing with a message on the lock is different. If you wish to open Messages to the list, you need to close it from the list screen.