Explanation

App1 present in RG1 and in RG1 there is no lock available. So you can move App1 to other resource groups, RG2, RG3, RG4.
Note:
App Service resources can only be moved from the resource group in which they were originally created. If an App Service resource is no longer in its original resource group, move it back to its original resource group.
Reference:
https://docs.microsoft.com/en-us/azure/azure-resource-manager/management/move-limitations/app-service-move