The trick is to sit on the toilet with the toilet seat brought up, and to use the towel to close the open area between your crotch and the toilet. Sort of sealing it for both sound and air.
The splashing sound gets 90% or completely canceled.
Bonus points to this technique are that it reduces the smell to the minimum too, because the air is trapped too.
The only thing to watch after is to not get the towel wet when flushing the water, but it doesn’t really matter since you should definitely drop it into the washing machine afterward.
