Google tried to sneak scoped storage into Android 10, but developers weren't having it. This more restrictive (and secure) method of managing your internal storage is coming back in Android 11, but there will be a new "all files access" permission. Or rather, there was supposed to be. Google has updated its support page to clarify that Android 11 apps won't be able to use that permission until 2021.
Scoped storage is designed such that apps can only access their own directories, as well as select shared spaces like Downloads. The current full storage access permission will go away, but Google hoped to placate developers with the "all files" permission. If an app really needs full storage access, developers will be able to add this permission at the cost of greater scrutiny from Google.
The new alert on Google's support page says that the Android 11 storage permission won't be available until early 2021, which Google blames on "COVID-19 related considerations." Presumably, this means Google is just running behind implementing the feature because of the impact the pandemic has had on productivity. Instead, Google recommends that developers who need that permission continue targeting Android 10 (API 29) with the legacy storage permission. Developers that can make do with scoped storage can update to API 30 at their earliest convenience.