In Azure AD, is it possible to change the owner of a Windows 10 device?

You can change the owner of the device via PowerShell.

Add the new owner.

Add-AzureADDeviceRegisteredOwner -ObjectId <Device ObjectId> -RefObjectId <New Owner ObjectID>

Then remove the previous owner.

Remove-AzureADDeviceRegisteredOwner -ObjectId <Device ObjectId> -OwnerId <Previous Owner ObjectID>

You can find the device's "ObjectId" using the following command.

Get-AzureADDevice

You can find the owners "ObjectId" in Azure Portal or via.

Get-AzureAdUser

You can use the Cloud Shell feature in the Portal to execute the commands or you could install them locally and connect up.