I have the s10+ and it’s actually useful, as you can remap the double click on that button to open any app you like. But yeah single click, never happened intentionally.
EDIT: F yeah, I just checked the settings and you can decide if you want bixby activation on single or double-click. Now I’ve set bixby to double click and on single-click it opens my password manager. If you don’t select anything, it will do nothing on a single click.
The setting is under “Advanced Features” -> “Bixby Key” for me.