You can find the total number of active scenarios for an organization by going into its Scenarios tab. In this case, you can see that this organisation has 3 active scenarios:
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You can also go to your Organization dashboard, and see the number of active scenario there
And if you use the Enterprise version, you can go to Analytics, and filter “active” scenarios
You can only see active scenarios on a per-organization basis, so there isn’t a way to see all active scenarios across all your organizations. The way to see them should, however, be the same for orgs that you own or in which you’re an admin.