Did you get that log data from the Console app or the system log, or is that what appears in the Terminal window? If the former, then stay out of the Console app and disregard any system logs as they are worthless for troubleshooting macOS these days.
When you restart or shutdown the computer, do you have "Re-open windows next time" checked (or whatever the message reads)? If so, then any app or utility that is open when you restart/shutdown the Mac will relaunch the next time you start the computer. Try unchecking that option to see if the Terminal still opens next time you boot the computer.
Disregard the information about the shell message you see within the Terminal app as that is irrelevant if you don't use the command line.
If you are not launching the Terminal app yourself and the Terminal app is closed when you restart/shutdown the Mac, then it means some third party software is responsible and is poorly programmed since a user should never see the Terminal window. It could be just some poorly programmed app you installed, or it could be some malware. Is there anything else displayed in the Terminal window besides the message about the default shell? Is there a name or anything on the titlebar of the Terminal app (the bar at the top of the app's window) when it opens?
You can run MalwareBytes to see if any malware is detected.
To look for possible software issues, run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper. If you give EtreCheck "Full Disk Access" it will provide us with a bit more information including the summary of recent logs.
