Hi, I see the same behaviour in S22 plus for SMS and in a way it makes sense. Imagine that you receive an SMS from someone on SIM 1 number and you reply back to them with your SIM 2 number - although you will have one view of the conversation, the other person will have 2 separate views of your messages ( from SIM 1 and SIM 2).
You should still be able to change the SIM that you want to reply with. After you have opened the message, click on the 3 dots in the top right corner and change the SIM. Check if you have this setting in your phone.
For new messages that you compose, the default SIM is selected ( I suppose you also experience the same).