Apologies for delayed response on this.
AAD DS is not supported in the MSIX App Attach context due to the direction of the sync, i.e. AAD to AAD DS and not the other way around which is a requirement for App Attach. Refer this FAQ once.
You can use MSIX App Attach and Azure AD DS with a different storage solution. You can create a security group with the computer objects that will only live in AD and use that with an IaaS file server or Azure NetApp Files for the share permissions.
Hope this helps.
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