Suppose IntelliSense isn't working and an author must look up the C# TotalMinutes function on Microsoft Docs or the Java FileReader object in Oracle Docs.
Think about it this way, if IntelliSense was working, are you going to cite IntelliSense as well? If I was using a Dishwasher as part of an experiment, do I need to cite the Dishwasher's manual? You will soon realise that this is a ridiculous concept.
It is pretty clear that if you are using a feature that is part of the language, then referring to the official documentation isn't plagiarism because it is built into the tool itself, you just weren't familiar with its existence. If you need to cite the documentation, then should you cite Dennis Ritchie every time you write a C program? After all, he did create C.
However, if you were copying chunks of code into your software then yes you do need to cite it. Even outside of academia, it is still good etiquette to cite non trivial data structures/algorithms you use that you didn't create.