Regarding questions 1 and 2, please check the description below:
We recommend that you host your source code on github and use Azure Devops for continuous integration/continuous deployment (CI/CD). This is because Azure DevOps Public Projects aren't generally discoverable to the general public. A project member needs to publicize the URL for it to be found.
You could use Azure DevOps for free and open-sourced projects. An Azure DevOps Services public project provides support to share code with others and to support continuous integration/continuous deployment (CI/CD) of open-source software. Users aren't required to sign in to gain read-only access to many of the services.
You could refer to this document to view more detailed information about public project.
Because here from what I can see, I cannot use Azure DevOps in these cases. Is that correct?
Your understanding is correct. The entry of the Code of Conduct is to build a better Azure Devops and let our users get a better experience.