The Note phones have hardware and software in them to take advantage of their s-pen.
Saying that > basic tapping on a s9 screen should work but there will be no air commands etc.
I use a normal soft tipped stylus for my Galaxy Tab and is fine for simple tapping etc.
The s-pen stylus has more intelligence as a a note phone reacts to the amount of pressure you use and has a button for various uses.
My Note 9 s-pen also has Bluetooth in it.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.