Hi!. Now I think that "Bartless" would be about Bart having invisibility powers. It would be another sci-fi episode outside Treehouse of Horror. It would be strange if "Bartless" were about this:

Not all sci-fi-themed episode of The Simpsons must be from "Treehouse of Horror": "The Man Who Came to be Dinner" is a sci-fi episode about the Simpson family being kidnapped by aliens from Rigel VII and is not part of any THOH saga.
"Bartless" would be another episode inspired on fan edits, "Bart the Cool Kid" was inspired on edits with Bart wearing outfits from Supreme brand (parodied in the episode as "Slipreme") and I think that "Bartless" would be inspired on that "invisible Bart" edits from @TheInviSimpsons Twitter and Instagram account.
Well, Sideshow Bob will NOT appear in that episode, but I don't want spoilers from anyone, it's much better to know it only when the real and official synopsis and the promo images from "Bartless" are revealed in February. It's worth waiting.
On January 8, 2023, when I was sleeping, I dreamed with the promo images from "The Many Saints of Springfield", "Carl Carlson Rides Again" and "Bartless" on FoxFlash and Bart was invisible in the "Bartless" promo images. Well, a little part of that dream became true with the promo images from "TMSOS".
"Bartless" could be an elegant title for "Invisible Bart" (in my opinion).

Not all sci-fi-themed episode of The Simpsons must be from "Treehouse of Horror": "The Man Who Came to be Dinner" is a sci-fi episode about the Simpson family being kidnapped by aliens from Rigel VII and is not part of any THOH saga.
"Bartless" would be another episode inspired on fan edits, "Bart the Cool Kid" was inspired on edits with Bart wearing outfits from Supreme brand (parodied in the episode as "Slipreme") and I think that "Bartless" would be inspired on that "invisible Bart" edits from @TheInviSimpsons Twitter and Instagram account.
Well, Sideshow Bob will NOT appear in that episode, but I don't want spoilers from anyone, it's much better to know it only when the real and official synopsis and the promo images from "Bartless" are revealed in February. It's worth waiting.
On January 8, 2023, when I was sleeping, I dreamed with the promo images from "The Many Saints of Springfield", "Carl Carlson Rides Again" and "Bartless" on FoxFlash and Bart was invisible in the "Bartless" promo images. Well, a little part of that dream became true with the promo images from "TMSOS".
"Bartless" could be an elegant title for "Invisible Bart" (in my opinion).