Can we broadcast a TMap whose Key is a enum and value is a TArray using DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam ?

Yes it should work, TMap with inclusion of blueprint support now should be fully supported by all stuff that uses relection system, if you getting any errors because of it, submit bug raport, but first check if you doing everything right

I haven’t tested it. But, I found it on a tutorial website.

DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam( FGenerateMyDataDelegate, const TArray<uint8>&, MyData );