I did the refactoring in the following manner: I had a big storyboard and it was causing lag issues (M1 processor) so I sliced it in smaller parts, gave all scenes a storyboard ID and, by selecting those I was interested, I did Editor>Refactor into storyboards.
Later this day I tried running my project on an AppleWatch target, and the following issue was raised : "Storyboard referencing not available for iOS under iOS8". I managed a patchwork solution by branching my project, but is there a more senseful fix to this problem?