Anvil Docs | Scheduled Tasks states that
Scheduled Tasks run in the Published version of your app. When configuring Scheduled Tasks, make sure you’re using the ‘published’ version of your app.
That may have been true before Deployment Environments were created. It may still be true for an App where you have not explicitly created any Deployment Environment.
Now, Anvil Docs | Deployment Environments states that you can enable Scheduled Tasks for any environment, not just the Published environment. And my App Logs confirm that, in fact, they do run in every environment where they’re enabled, Published or not.