Does Linea Sketch require an Apple Pencil?
The short answer: No, not at all!
The long answer: Linea Sketch for iOS was designed from the ground up to harness the power of the Apple Pencil and the iPad Pro. However, not everyone owns this amazing combo and we recognize that. The good news is that you can use your finger or a third party stylus to draw on supported devices, you just won't be able to use additional features such as pressure sensitivity and tilt control.
While there is no formal list of supported stylus, you should have no trouble using one with Linea Sketch.