If you are a Microsoft Stream administrator (and by default global tenant Microsoft 365 administrators are), then you can select the Cog in the top right of the Stream page and then select Admin settings as shown above.
Then on the left hand side you’ll be able to select Usage details under the Manage Stream heading. This will then show you a report of how much data your videos are currently consuming. When your organization purchased Microsoft Stream, you received 500 GB of base storage and an additional 0.5 GB of storage per licensed user. If you need additional storage for your Stream content, you can purchase one or more 500 GB storage add-ons.
You can also select the Recycle bin option, also on the left, to recover any videos that have been deleted for 30 days.
There are plenty more administration options inside the Stream admin area, so go and check them out!