LINQ remove rows from source datatable using match from another datatable

How to remove all rows from dt1 where dt1.user is found at dt2.username. Schema is different between datables

We can reformulate as: Get all dt1 rows where dt1.user not is present in dt2.username

Assign Activity
Result | List(Of DataRow) =

(From d1 In dt1.AsEnumerable
Where Not dt2.AsEnumerable.Any(Function (d2) d2("username").toString.Trim.Equals(d1("user").toString.Trim))
Select r=d1).toList

then based on the filter result we can copy it to a datatable or clone the origin one
check within an if acitvity
Result.Count > 0
Then: dtResult = Result.CopyToDataTable
Else: dtResult = dt1.Clone