According to https://fountain.io/syntax/#boneyard
anything between /* and */ will be omitted from the PDF file.

If I generate the PDF in Visual Studio Code's Better Fountain extension, it works but as soon as I import the .fountain file to STARC, the section that should be invisible is some RIGHT aligned weird-looking thingy.

Fountain is a widely used application, it may be a good idea to check all its features at https://fountain.io/syntax/ and whatever does NOT seem to work when imported to STARC, should be fixed.