How Vecna is suddenly able to open portals to the Upside Down in season 4 is explained by a crucial fact that the Stranger Things season 4 finale missed.
The season finale of Stranger Things season 4 made a suggestion on an unanswered query regarding Vecna, the antagonist. In Stranger Things season 4, volume 1, Vecna’s actual identity as Henry Creel or One, a potent psychic with a plethora of terrible talents, was made known. Nevertheless, Vecna didn’t seem to have the ability to create portals to the Upside Down prior to Stranger Things season 4.
The psychic link made by killing unstable youths was used in Stranger Things season 4 to expose Vecna’s grand plot to drive the Upside Down into Hawkins by creating enough tiny portals to create a sort of tear between the two realms. He appears to require four killings and four gateways in order to carry out his intentions. He has accomplished this at the conclusion of Stranger Things season 4, and the season finishes with the Hawkins crew watching in horror as the Upside Down seeps into Hawkins.
Earlier seasons had Vecna acting entirely through already-existing portals in Hawkins. In early seasons of Stranger Things, Vecna refrained from attacking the teenagers in Hawkins because he was unable to create his own portals. One steals the power of whatever he consumes, and Eleven is the only character in the series to be revealed to have this capacity. This revelation is essential to understanding One’s strategy in Stranger Things seasons 3 and 4. Vecna’s link to the outside world was only tenuous when Eleven sealed the large entrance to the Upside Down in season 2.
He used this relationship to grow close to Eleven so he could bite her, which he eventually succeeded in doing in season 3, episode 7, “The Bite.” The Mind Flayer’s flesh monster grips onto Eleven’s leg and buries a portion of itself inside of her. After tending to the wound, it was revealed that Eleven’s cast-off blood reacted to Flayed Billy’s presence, indicating that the hoped-for link has been made and Vecna is now able to operate his own portals.
What the Vecna’s Portals Change Means For Season 5 Of Stranger Things

In the Stranger Things season 4 finale, Vecna explained to Eleven that he wanted her abilities so he could carry out his plans without interference. There is no way to predict what Stranger Things season 5 will include since he was no longer imprisoned in the Upside Down. The Upside Down is presently leaking out into the real world all around Hawkins through a large active gateway. Vecna’s capacity to establish new portals may, however, provide access to less-known but potentially more terrifying creatures.
The greatest entrance to the Upside Down yet was revealed at the end of Season 4 of Stranger Things, engulfing the whole city of Hawkins. Vecna may now open additional portals as he pleases, thus even if the Hawkins team locks all the known Upside Down gates, it won’t be enough to thwart his goals; he will need to be dealt with in a more long-lasting way. It’s probable that Vecna will have to be put to death if the Hawkins gang is to make it through the upcoming Stranger Things season.