I cannot clone a simple repository from Azure DevOps. OS: Ubuntu 18.10
I do this:
Ensure you are a member of the Contributor group and that your permissions are not limited for your user or group on the azure repo.
Azure Contributor group has per default permission to clone, fetch, and explore the contents of a repository; also, can create, comment on, vote, and contribute to pull requests.
Any of this permissions can be edited by members of the Project Administrator Group or those having Manage permissions set to Allow for Git repositories as described here.
If your group or user does not have the permission to clone the repository, you will get the behaviour described by the question.