It sounds like you're combining elements from "Star Wars" lore and gameplay mechanics from "Star Wars Jedi: Fallen Order." While Darth Maul is a well-known Sith character with his iconic double-bladed red lightsaber, in "Jedi: Fallen Order," players don't directly interact with him or acquire his specific lightsaber setup within the storyline.
However, your suggestion of customizing a lightsaber in Journey Plus mode on Dathomir is interesting! In "Jedi: Fallen Order," players can indeed find various lightsaber components and colors to create their unique styles, but the lightsaber customization mentioned doesn't directly include Maul's specific design.
If you are playing Journey Plus after completing the story, you can customize your lightsaber and give it a red crystal and various components to reflect your favorite Sith aesthetics. Choosing a Power and Control emitter and a Peace and Justice switch might give it a unique look, although it's a creative mix since Peace and Justice is typically associated with the Jedi.
If you're looking for ideas on how to build a lightsaber inspired by Darth Maul or more about different customization options in "Jedi: Fallen Order," feel free to share!