During the course of the sequel trilogy viewers were introduced to a new group of characters called, The Knights of Ren.
We came to understand (The Force Awakens, The Rise of Kylo Ren Comic) that after Ben Solo turned to the dark side and became Kylo Ren, he was inducted into the group and seemingly became their leader, as Snoke once refers to him as "The Master of Ren", and therefor it appears both were answering to Supreme Leader Snoke. Also The Last Jedi mentions they were on a mission, being absent from the film.
But the final film of the sequel trilogy, The Rise of Skywalker, very ambiguously gets into notions of Palpatine's and potentially, "The Sith's" return...
Early in the film Kylo Ren and the Knights of Ren seem to be working together, as Kylo finds the first Wayfinder (Sith Holocron) with their help and then later, they capture a well-known character that plays into what Kylo Ren was trying to do to get closer to Rey.
But once Kylo Ren returns from the Dark Side and once again attempts to be Ben Solo, he goes back to Exogal presumably to help Rey face Darth Sidious. However, once he arrives on Exogal, he must face The Knights of Ren, before being able to enter the deeper chamber and throne room.
So does this mean that The Knights of Ren were always aligned with Darth Sidious?