This is exactly the kind of workflow gap we keep seeing with AVD RemoteApp deployments: users need to move files between the local endpoint and the hosted app naturally, especially with ERP, CAD, document management, Outlook attachments, and legacy line-of-business apps.
Disclosure: I work on TwinPane, a tool built specifically for this file workflow problem in AVD/RDS/Citrix environments. It does not add native AVD drag-and-drop, but it lets users access local folders from inside the remote session and open remote files in local apps without relying on normal drive redirection.
Native drag-and-drop in AVD would still be great to have, but for teams blocked today by RemoteApp file workflows or disabled drive redirection policies, TwinPane may be a practical workaround.
https://twinpane.com