Warning: SPOILERS for Star Trek: Picard Season 3, Episode 4 - "No Win Scenario"Star Trek: Picard season 3's Changeling storyline has finally answered whether the Borg ever encountered Star Trek: Deep Space Nine's Dominion Founders. The Changelings made a shock return in Picard season 3, episode 3, "Seventeen Seconds", when it was revealed that a rogue schism was behind the theft from Daystrom Station, and the sabotage aboard the USS Titan-A. Commander Seven of Nine (Jeri Ryan) and Jack Crusher (Ed Speelers) unmasked the Changeling saboteur aboard the Titan, and in "No Win Scenario", Seven continues to track the imposter with help from Captain Liam Shaw (Todd Stashwick).
Shaw is aware of the Changelings from the time of the Dominion War in Star Trek: Deep Space Nine, whereas Seven has never encountered one. As the Dominion were forced to withdraw from the Alpha Quadrant prior to the USS Voyager returning home, this isn't surprising. However, Seven is a former Borg drone, and her lack of knowledge about the Dominion and their Changeling Founders definitively answers whether the Borg encountered the Changelings.
Picard Season 3 Answers Whether The Borg Met DS9's Changelings
The Borg Collective is a hive mind, that shares knowledge of the species they encounter across a vast neural network. As a former Borg, Seven would have access to information about every species that the Borg encountered and assimilated into the Collective. The fact that Shaw has to give Seven advice about how to locate the Titan's Changeling impersonator by asking them specific questions, or stealing the "pot" the Founders use to regenerate in their liquid state, makes it clear that the Borg never assimilated this crucial information about the Dominion's Founders.
Seven was separated from the Borg Collective in 2374, during which the Dominion War was still ongoing in the Alpha Quadrant, so it's still possible that the Collective eventually encountered the Changelings. However, Seven retained a nascent connection to the Borg Collective which Captain Kathryn Janeway (Kate Mulgrew) used to her advantage in Star Trek: Voyager. Therefore, it's highly unlikely the Borg encountered the Changelings during the time that Seven had access to the Borg hive mind, if at all.
Could The Borg Beat DS9's Changelings?
It's clear from Star Trek: Picard season 3's Odo reference that the Changelings have been divided in the wake of the Dominion War. The Great Link has likely embraced a more benevolent society, when before they had sought to subjugate the Alpha Quadrant to bring order to the universe, based upon their distrust of the Solids. During the height of their powers, it's likely that the Changelings would have never let the Borg Collective get anywhere near the Great Link, using their considerable Vorta and Jem'Hadar forces to repel the advancing Borg Cubes.
Star Trek: Picard has now confirmed that no such encounter has ever taken place, but it has been theoretically proven that the Borg could assimilate DS9's Changelings. It's unsurprising that the two mighty Federation enemies never met, however. During Star Trek: Deep Space Nine's Dominion War, the Borg Collective advanced on Earth, intent on sabotaging First Contact and changing history. When Captain Jean-Luc Picard (Patrick Stewart) and the crew of the USS Enterprise-E foiled their plans, they presumably retreated back to the Delta Quadrant to reconsider their plans as the Dominion War raged across the Alpha and Gamma Quadrants.
Star Trek: Picard Season 3 streams Thursdays on Paramount+.