git push newremote refs/remotes/oldremote/*:refs/heads/*

This command will push all branches from the oldremote to the newremote. The refs/remotes/oldremote/* part specifies that we want to push all branches from the oldremote, and the refs/heads/* part specifies that we want to push them to the newremote as branches.

For tags, that would not be so much complex, just git push newremote --tags would be enough.

Found at https://www.metaltoad.com/blog/git-push-all-branches-new-remote.