Original answer:
Hi @curious7 I was able to reproduce the issue you described. I assigned the Microsoft 365 E5 Developer (without Windows and Audio Conferencing) license to a user that was previously unlicensed. When I logged in to the Microsoft 365 portal as that user there were no apps available.
You also need to add the Office for the Web license and SharePoint (Plan 2) in order for the user to see the apps available in the web portal.
As to your other question:
Microsoft Stream (Classic), which will be retired February 15, 2024 and replaced by Stream (on SharePoint), can be blocked using the Azure portal. Refer to the following article to learn how:
https://learn.microsoft.com/en-us/stream/disable-user-organization
Microsoft Stream (on SharePoint) cannot be disabled in the same way as Microsoft Stream (Classic). It acts as a sort of one-stop shop for videos uploaded to OneDrive or SharePoint. You can however restrict file types (such as videos) from being uploaded to SharePoint or OneDrive. Refer to the following article to learn how:
https://learn.microsoft.com/en-us/sharepoint/block-file-types