When the credits rolled for Star Wars: The Rise of Skywalker, viewers had a lot to digest regarding the fate of their protagonist. Rey was revealed to be a Palpatine, gains some form of closure with Kylo Ren and creates her own lightsaber that takes on a different color than any of her Jedi counterparts. Lightsabers are unique weapons made by their Force users, and they often reflect the path their creator chooses. So far, the Jedi and Sith Rey deals with have had red and blue sabers; however, Rey's lightsaber is yellow and made from the staff that she carried throughout the series.
Speculation based on Star Wars lore can give fans an idea of what the yellow saber could mean to Rey; however, concept artist Matthew Savage posted on his Instagram the prop and its inner workings. From this, it appears Rey's lightsaber is a single-blade, despite speculation from fans that it could've been double-bladed.
Rey wielding a double-bladed lightsaber made sense to fans given how comfortable she feels using the staff as a weapon, and it isn't until she starts to learn the Jedi ways that she starts to use a new fighting style with the lightsaber. With that in mind, the lightsabers she uses before her own are single-bladed, but they are bonded to other Jedi and represent their paths, not Rey's.
The lightsabers she uses prior to her own are connected to Luke and Leia, and they reflect their journeys, even in the color of the blades. It takes a kyber crystal to create a lightsaber, a crystal that is initially colorless, but the lightsaber eventually takes on a color when it bonds with its Jedi or Sith, with each color representing different classes. The yellow lightsaber is traditionally used by a Jedi Sentinels, a school of thought that embodies both the Consular and Guardian Jedi philosophies.
Jedi Sentinels are those Jedi who mix both the civilian world and the Jedi tradition, two traditions that are often in conflict with each other. The Jedi tradition has always been to be detached from society, family and romantic relationships since these things can lead a Jedi to the dark side of the Force.
In contrast, Jedi Sentinels are more balanced. The Sentinels don't believe that a Jedi has to follow rigid tradition to be a Jedi and that the only path to the dark side is one of choice. The Jedi Sentinel have other things that often set their lightsaber apart from other Jedi, which includes them often being double-bladed.
Jedi Sentinels don't have a written rule about double-bladed lightsabers, but they're more common with Sentinels, as shown in their various appearances in The Clone Wars. However, as far as audiences know, Rey knows nothing of the Sentinel tradition, so the fact that traditionally yellow lightsabers are often double-bladed wouldn't affect her decision in her lightsaber creation.
While the final lightsaber isn't a double-blade, which suits both the tradition of yellow sabers as well as Rey's fighting style, it is still connected to her staff, being made by parts of her original weapon. Another aspect of her lightsaber that's caused some fans to question it is the color.
Rey's yellow lightsaber isn't a reference to a subplot in the story, but it is a reflection of her personality, which aligns itself with the aspects of the Jedi Sentinel; however, some fans have critiqued her lightsaber color since her mentors' lightsabers are blue in the sequel trilogy, and if she chose to go down the same path as them, then her saber should match theirs in color. Furthermore, when Rey is asked who she is, she replies, "Rey Skywalker," which further shows she's choosing the path of her masters, Leia and Luke; however, her saber is uniquely her own.
There's much to learn about Rey and the path she's chosen, like how it differs from the Jedi before her. The double-bladed lightsaber is undoubtedly a cool thought, but as far as Matthew Savage's design goes, it's clear it was intended to be single-bladed despite how practical a double-bladed saber would be for the staff wielding Jedi. With that in mind, Rey's yellow, single-bladed lightsaber reflects her beliefs and show she's not one to follow any pre-established path to a T.