My bidet comes with a butt dryer, aka a mini hair dryer pointing at your ass. It works decently but takes some time. Some people do indeed use towels. It’s not that gross as the bidet is quite good at getting everything off. I’ve even seen people using white towels without ever a mark on em.

I just use the butt dryer most times, have some toilet paper on hand if i need to dry quickly, i essentially never buy it as I’ve been on this one bulk costco pack for over a year