The Changelings' ability to change their form at will would enable the Borg to blend in seamlessly with other species, making it easier for them to assimilate new technology and knowledge.
The Borg are constantly trying to better themselves. Earth Technology, Earth weapons beat them back many times...so they would become better with our weapons and technology.
According to Seven of Nine, there's a simple reason for this; the Borg encountered a Kazon colony, but "their biological and technological distinctiveness was unremarkable." It seems the Borg considered the Kazon to be "unworthy of assimilation." In their view, the Kazon would not add anything to the Borg Collective; ...
Jack Crusher was a pivotal character in Star Trek: Picard season 3. The son of Jean-Luc Picard and Dr. Beverly Crusher (Gates McFadden) was revealed to be the linchpin of the Borg Queen's (Alice Krige) plot to assimilate Starfleet, evolve the Borg, and exact revenge on the United Federation of Planets.
What Happened to the Changelings? History and Lore of Star Trek Villains'
Is Jack Crusher part Borg?
Jack suffered from terrifying visions and hearing voices as a child, but it was Beverly who ultimately determined that her son was born with organic Borg DNA he inherited from Jean-Luc from his time as Locutus of Borg.
Jack is indeed the biological son of Jean-Luc Picard and Dr. Beverly Crusher, but as much as he wanted to deny it, the young Crusher is also the son of Locutus and the Borg Queen, who pondered Latin names for Jack like Regenerati (Rebirth) or Puer Dei (Child of God) before she chose to name him Vox.
Species 8472: Also known as the Undine, they were a highly advanced and biologically unique species from fluidic space. Due to their vastly different biology, the Borg were unable to assimilate or adapt to them.
The Borg quickly realize that Species 8472 is immune to assimilation and that contemporary Borg technology is no match for it. In fact, 8472 is one of the few species so advanced that its ships are able to destroy Borg cubes in seconds.
Warning: Spoilers for Star Trek: Prodigy Season 1, Episode 12 - "Let Sleeping Borg Lie"The Borg returned in Star Trek: Prodigy season 1, episode 12, and the cybernetic villains proved they have the power to potentially assimilate Star Trek: Deep Space Nine's Changelings.
Officially, the existence of a Borg homeworld is a hypothetical one as it has yet to be revealed in a canon Star Trek source. However, an identity for the Borg homeworld is given by the non-canon novel Lost Souls, which names it Arehaz.
Only one Queen exists at any given time; when she is destroyed, a new Queen takes her place. In Star Trek: Voyager, it's revealed that the Borg Queen isn't a singular entity, but the name given to any that serves as its host, possessing all previous Queen's collective consciousness.
As crew members beamed on and off their ships, the computers recognized this new genetic code as "common biology" and integrated it into the DNA of every officer in the fleet. The Changelings wanted Jack because of they needed his Borg-altered DNA, though they later ended up acquiring this from Picard's body.
Could "Q" or a "Founder" be assimilated by the Borg? Yeah, maybe. There seem to be some species like species 8472 though, that are just incompatible with assimilation, but for the most part they can usually find a way to assimilate many species.
After his assimilation in the Star Trek: The Next Generation two-part episode, "The Best of Both Worlds," the Borg created an abnormality in Picard's parietal lobe. The Changelings and Borg devised a plot to steal Picard's human body and use his Borg DNA to assimilate Starfleet.
The Borg learn everything they know about an enemy through assimilating beings. The Borg couldn't assimilate Species 8472 because their immune systems were hyper-advanced.
It is fairly likely that they cannot, due to their shape-shifting nature, and their natural state of being not being corporal. However, they could still be destroyed fairly easily due to another shortcoming the Founders have against the Borg: a single point of failure.
The Borg would become an unstoppable force, able to assimilate or simply change the galaxy to fulfill their vision of perfection. In addition to gaining all the knowledge of a particular Q, having their consciousness uploaded to the Borg collective, they would also potentially gain the god-like power of a Q.
He was assimilated by the dying Borg Queen and named Võx. New technology added to modern Starfleet vessels allowed these new Borg to assimilate the ships in moments. Using a rebuilt USS Enterprise-D, the command crew of that vessel saved Jack and destroyed the remaining Borg, seemingly defeating them once and for all.
Q. The Q are potentially the least likely to get assimilated, for not just one reason but two. Firstly, their near omnipotence and god-like powers would make it almost impossible for a Borg, or even all Borg working together, to capture a Q.
There were plenty of theories about why Jack could do these strange things. The red eyes and psychic powers seemed to indicate Deep Space Nine's Pah-Wraiths, especially given the Changeling connection.
The most likely reason for Wesley's absence is that, in writing these final episodes, the decision was made to focus on the impact of Jack Crusher's existence on Jean-Luc. This is the final chapter of Jean-Luc Picard's story, so the focus on his legacy and his own next generation makes sense.
