Hi @Kira ,
Could you also point out to the referred Forum links here, so that we can analyse or compare and see what you have missed out. Maybe a thorough check again on those links would help you to resolve it.
But notice that there are some specific differences to keep in mind when it comes to updating using Linq.
In terms of Datatable update and with Assign activities, a recreation of the Datatable with the updated values need to take place.
We can also update the same reference or variable using Invoke Code activity and calling the methods on the datatable reference variable.
More on this topics you could find below :