The Terminal plist isn't involved here. The other reset operations are also not applicable.
There's an error somewhere in one of your Terminal.app login-related files.
It looks like a problem with the control sequences in the login used set the prompt string PS1. If the following exists, remove it.
export PS1='{something-not-quite-right-here}'
Start here for the clean-up sequence, quite possibly creating a new and then using a second admin user...
Terminal Not Functioning Properly - Apple Community
Some of the following files may or may not exist, but the following will get all of the files out of the way. This for the original login user yourshortname in the following example. There are other ways to do this more easily by using ~ syntax, but the following shows what's happening without any shortcuts...
sudo mv /Users/yourshortname/.bashrc /Users/yourshortname/old.bashrc
sudo mv /Users/yourshortname/.bash_profile /Users/yourshortname//old.bash_profile
sudo mv /Users/yourshortname/.bash_login /Users/yourshortname/old.bash_login
sudo mv /Users/yourshortname/.profile /Users/yourshortname/old.profile
It's also possible to rename these same files using Finder from the original login. Select ⌘> to enable viewing hidden files, then rename the above four files, or whichever of the four exist. Select ⌘> to toggle off hidden-file viewing in Finder.
