Migrate Git repositories & associated pipelines between Azure Team projects
I am afraid there is no such out of box way to achieve this at this moment.
There is a Under Review user voice about it:
Explore how to move git repositories between Team Projects with full-fidelity history
With above document, we could migrate git repositories to anther team projects with full-fidelity history.
However, we could not do much more for those associated pipelines. There is no such way to get all the associated pipelines directly. To resolve this, we need use powershell scripts and REST API Definitions - List to traverse all the build definitions and find out that the repo name is the build definitions of the specified repo.
Then, use the REST API Definitions - Create to create a new pipelines in another team project.
You could check this thread for some more details.
Hope this helps.