Option to Multi-select devices while creating Re-occurring maintenance window

There is a request to provide an option to select multiple devices (multi-select) which are of different categories/sites/strategic groups while creating Re-occurring maintenance window.

Currently, the user has to create a functional group and then add the required devices to it.

The use case is, if the customer has to select 5 to 10 devices belonging to different groups, then there is no other way except creating a functional group.