If you removed the ash forest sequence from the beginning, but still wanted to include Mustafar in the film, you could reuse a shot from Rogue One to create a new establishing shot of Vader’s castle for the scene where Kylo has his mask reforged.
Also, does it really make sense that Vader would have the wayfinder? I feel like Exegol would’ve been a secret Palpatine kept from Vader.