Hi there @Andrey_Kovalev
C# is supported in ‘Invoke Code’ (if at all you have had to use large chunks of code then it would be invoke code as all the other activities have one liners which are easy to replicate in VB)
Also importing the assembly Microsoft.Csharp will fix most issues (if it doesnt hen manually add the assembly reference by opening the xaml in notepad)
PS : I use Csharp code all the time with version 2018.4.5