Just wondering if this is posssible and how to do it?
There's no concept of 'default terminal app' in macOS - what effect do you expect changing it to have? When other apps are trying to invoke the terminal, they are executing stock Terminal.app directly.
On macOS, you can set default apps ("filehandlers") for specific filetypes.
Eg. You always want a .txt file to open in VSCode, so you set VSCode as the default filehandler for .txt filetypes.
There are some filetypes, like .sh, that may or may not open in the operating system's default terminal (Terminal.app) but even then it is acting as a filehandler for that filetype via file association ("Always open with..").
If a terminal is invoked by another application, it will usually specify Terminal.app since that is installed on every Mac. You may be able to change the specific terminal application invoked on a per-app basis in the settings of an app... or you may not.
Hope that makes sense.
Here's the setting of a default terminal in VSCode:
