I guess this could be because you are using the SQL Edge edition, and Azure Data Studio may not be geared up for support of Restore on Edge yet. Restore Database comes up as a preview feature in my Azure Data Studio (on Windows for regular SQL Server.)
But you can always restore a database like this:
RESTORE DATABASE mydb FROM DISK = 'yourpath'
If the backup comes from elsewhere or you want to restore the backup under a different name, you need to add the WITH MOVE clause to specify the location of the database files.
At this applies to "regular" SQL Server. I have not worked with the Edge version, but I would expect the RESTORE command to be the same, at least for the basic stuff.