In the modern series, are Transformers supposed to exist? They did appear in the old issues (90s G2 crossover) as guests but I remember seeing a preview of an issue of the modern series in which the movie version of the Optimus Prime was being sold as a toy in a toys shop. Either they made in-universe toys of the "real" Transformers or Transformers are fictional in the new series. Does the new series take place in a different universe than the old G.I Joe comic?
The GI Joe: Special Missions side-comic established Transformers to be fictional after the original crossover miniseries, but that was "soft-retconned" in the G2 crossover. But since the Transformers are never referred to again after that, you can assume that the G2 crossover takes place in its own "mini-continuity" separate from the rest of Marvel GI Joe.