We used Awl Grip Griptex on some interior steps. Worked great. There are various YouTube videos on how to apply. You don't need much.
“If you have a router , place holly strips on the tread ,leave them proud by 3/16 or so.”
I like that. Would really make those stairs pop. Not that hard either.
does that have sand in it?
I remembered we used a product like this in a tub once and it worked well even though it was smooth to the touch.
Tub Grip Clear anti-slip bathtub coating.