I recently found the Kylo vs Vader fanfilm. I think one editor a while back borrowed something from this for a Force Awakens edit, but I think it could be integrated into Rise of Skywalker fairly easily and be used to inform the audience of a lot of Kylo’s motivations. You could also push his journey to Exogal up to follow from it
Here’s what I came up with (password: fanedit)
Beginning
Ending