The helmet figured heavily in concept art for The Force Awakens, and even was considered as part of the marketing for the film (It does show up in the second trailer but originally it was considered for teaser posters, figure box art etc).

In TFA we see Rey touching the Anakin/Luke saber which sets off a force vision. Some speculation has stated that perhaps a similar vision happened when Ben touched Vader's helmet, and that's what he's been referring to when he's saying "Show me the power of the dark side".

It's possible that part of Rise of Skywalker is set on Endor,(judging by the DS wreckage)....and presumabely that's where Ren recovered it from, unless Luke for some reason took it somewhere else after the pyre.

The helmet was last seen on Ren's destroyer The Finalizer, which was also seen in The Last Jedi (It's the ship Hux commands at the beginning of the film), but it's unclear if it was still onboard or even if the Finalizer was one of the ships that was destroyed. (The Finalizer's captain is seen on Ren's shuttle at the end of the film)

So I'm wondering if there might be more to the helmet in the grand scheme of things?