Use bare return, don't add that print() statement
Edit: I flagged your comment as spoiler as it might gives a hint to the other warriors

Have you tried adding the relevant import statement to the top of your solution - using System.Collections.Generic;?

i'm using C# btw

src/Solution.cs(8,13): error CS0246: The type or namespace name 'List<>' could not be found (are you missing a using directive or an assembly reference?)
src/Solution.cs(8,37): error CS0246: The type or namespace name 'List<>' could not be found (are you missing a using directive or an assembly reference?)

Which language ? What do you mean with the compiler would not detect List variable? This kata has been solved about a 150_000 times, it's reasonnable to suppose your code is the culprit a priori... Or please give clear examples of fails.

sTriangle_ValidPostiveNumbers_ReturnsTrue
Test Failed
Expected: True
But was: False

this is the only error i have from all 10 run test. what could go wrong?

How can the compiler didn't detect List variable? it's working in my VS2019! And it disemvowel really well.