S Pens for phones and tablets are interchangeable.
You can use S Pens made for Samsung phones on Samsung tablets that support the S Pen, and vice versa.
The nibs are also interchangeable. So you can buy any S Pen nibs online and use them on any S Pen.
There are different types of S Pen nibs though. The original nibs from Samsung S Pen actually comes with a rubber/matte texture tip on the nib. It's difficult to see but it's there to provide the extra friction, or maybe it's there to dampen the tapping sound while writing.
The S Pen nibs sold online are just plastic nibs with hard plastic tips. If you want the rubber/felt tip, you'll have to get the original Samsung S Pen nibs.
In terms of writing and drawing performance, there's not much difference between the non-original vs original nibs. The hard plastic tips are slightly smoother, which is better for writing.
The S Pen nibs are too long for the Staedtler Noris Digital in case you're wondering. You can still write but you won't want the nib to break because it's difficult to get a broken nib out from the holder.