The 4th Wall is defined as the imaginary barrier that separates the characters from the audience. However, in The HV and Dino-Weapon Show, the 4th Wall is a real, tangible object that allows the audience to see the action. In the episode "Dino-Weapon and the Kirbo Problem," Dino says that UXW allows the 4th Wall to exist in the first place, as well as allows the audience to see the action in real time. Despite this, we never learn if the 4th Wall is actually just a camera or if it's something else.
Gaming Videos: During the gaming videos, either Dino-Weapon or The Editor will ask if the "camera is rolling," which has been confirmed to be OOU commentary to make sure the camera is working, as is standard nowadays.
Sans's Shorts: Stupid Sans is aware of the 4th Wall, and speaks to the audience behind it in nearly every one of his shorts. The most direct interaction is in his short "Where Blaster?" where he headbutts the camera and comments on the show not "being a movie or anything like that."
Dino-Weapon and the Kirbo Problem: In this episode, Dino, Kirbo, and Glue Bunny are all shown to be aware of the 4th Wall and spend some time determining what shape the screen is, with them concluding that it has no clear shape.
Dino's Paradox Explanation Attempt: This video is a metaphor that is supposed to clarify the barrier between the characters and audience. After the audience member attempts to break the screen with a magic hammer of some sort, the entire device starts turning transparent as reality starts distorting, with Dino explaining that breaking the barrier would be catastrophic, not to mention impossible in the first place as no fictional or real character can break the 4th Wall without destroying the screen and disabling the connection between both dimensions.
This theory stems from the in-universe idea that movies are random circumstantial events that happen to be caught on camera. During certain moments in some videos (mostly gaming ones), either Dino-Weapon of The Editor will ask if the "camera's rolling." These comments have been confirmed to be non-canon, and are accidental OOU (out-of-universe) remarks to make sure nothing's wrong. However, Stupid Sans says in his Short "Where Blaster?" that "at least this isn't a movie or anything like that," showing that he is aware of the 4th Wall and its functions. These pieces of evidence essentially debunk the random events theory.
This theory is interesting because even though Null is talked about quite a lot in the series, we never get to see any Null contraptions or photos. However, Null wasn't discovered until 2012 (according to the series), and Dino-Weapon explains to Kirbo that he originally was an animatronic for a separate version of Earth in 1988. He also explains how that particular Earth was almost a 1-1 replica of Main Earth, except for the fact that Dino's Earth was only a few seconds behind Main Earth's time. This was when Dino found out about the 4th Wall, and that UXW explained to him that the 4th Wall can't be changed chemically, and it can't be literally broken because it's just too strong. UXW has then went on to study the 4th Wall, and discovered that there were no traces of Null anywhere.
This comes from the fact that screens are almost always rectangular, with exceptions being screens from select dimensions. However, this was debunked by Dino-Weapon when he showed Glue Bunny and Kirbo the 4th Wall outright and they commented on how its shape was undefinable.