No. There are lots of stories about various very long versions of Dune. The most common story that is Lynch had a 6-hour version and that the studio forced him down to 2. It's a myth. The theatrical cut is the only cut Lynch did.

IIRC Lynch did not have final cut on Dune, and was so bitter about it he never made a film he wasn't contractually allowed to edit himself again. If you look at the deleted scenes, they show Lynch was going for a very different tone to the finished product.

The "6-hour version of Dune" is probably confusing the Lynch treatment with Jodorowsky's attempt at a Dune film -- which was never filmed (the script wasn't even finished!), but whose production was documented in the 2013 Jodorowsky's Dune:

https://en.wikipedia.org/wiki/Jodorowsky's_Dune

It may also be confusing Lynch's film with the 2000 Sci-Fi miniseries Frank Herbert's Dune, which totalled roughly 5 hours across three episodes.

Possibly, but the rumours of a 6-hour and even longer cuts go back years. I remember discussing this way back in the late 1990s. It's a very persistent rumour.

The attempted Jodorowsky treatment was in the 1970s. The documentary film was more recent, but people certainly would have heard about it at the time.

There was never a four hour version. It doesn't exist - there's a version with a bunch of filmed material and storyboards of what might have been filmed, but that's it.

That version with commercial breaks is almost four hours, which probably feeds the rumors. I've seen that version on television.