https://learn.microsoft.com/en-us/dotnet/api/system.collections.immutable.immutablelist.toimmutablelist?view=dotnet-uwp-10.0&viewFallbackFrom=netcore-3.1
ImmutableList.ToImmutableListTSource(IEnumerableTSource) Method (System.Collections.Immutable)...
Enumerates a sequence and produces an immutable list of its contents.
methodsystemcollectionsimmutable