In server you can go to the Administration section, select Projects, and get an issue count per project. Specifically an at-a-glance view of the number of issues in each project in a list form, as provided in Server. The issue count is missing in Cloud, it seems.
Querying each project individually is not really the best option. In addition to requiring much more manual work (we're not talking 2 or 3 projects) theres also the question of whether or not the results can be trusted, if browse permissions are not set, or if there is issue-level security in use.