Azure DevOps Organization is not visible or not showing up!
There are many reasons why an Azure DevOps organization may not show in the list of organizations when you login into Azure DevOps. The reasons may be as follows an Organization would have been already deleted or you have been removed as a user of the Azure DevOps Organization or it would have simply moved into a different tenant (different Azure Active directory) for which you may not have access to.
Incase if the organization has been moved to a different Azure Active Directory tenant then reach out to the Administrator of the tenant and ask him to move the Azure DevOps org to the old tenant. Otherwise you can also ask the admin to add yourself as a user of the tenant.
If any of the above is done then you would get to see your Azure DevOps organization again. Incase if it has been deleted then you may need to do the steps to restore an Azure DevOps organization that has been deleted by another Project Collection Administrator or Org Administrator.