IAsyncEnumerable is a type that was introduced in netcoreapp3.1 times. While somewhat an enumerable (even though async in nature), it never had the capabilities as its synchronous counterpart. Until dotnet 10! Now we have some feature-parity between those two.
Recently, there were two new features merged in .NET 10 I think are small little quality of life improvements: Avoid Blocking on startup with BackgroundServices and a new string comparer.
LINQ has a Join operator, that basically translates to something like a SQL INNER JOIN. There is no built in operator for a LEFT JOIN in LINQ, but you can achieve the same result by using a combination of GroupJoin, SelectMany and DefaultIfEmpty. But there is a chance that this might change in the future, as there is a proposal to add a LeftJoin operator in .net 10.