I feel like a better title for this would be "Star Trek: Retcon." Not only have they been retconning the established history of Star Trek, they've retconned their own show as they go. For example, Lt. Cmdr. Airiam was never really established as a character, really just a visual, so they added all her backstory in the same episode they killed her off. She never showed any emotion (not they they ever really gave her many lines or opportunity to do so), but all of a sudden, we find out she's not only capable of emotion, and had close relationships with the other crew, but a human (humanoid?) that had extensive cybernetics to enable her to live. Apparently, it was established in episode 3 of "After Trek" (which I've never watched) that she was an "augmented alien." I still think they originally intended her to be an android, but the fact that Data was already established as the first android in Starfleet, they decided to change her backstory to avoid conflict.
Other retconning:
Klingons - Changed their look (again). This isn't out of the ordinary in Trek; obviously, the Klingons and other races have been changed visually in the past. But ST:Ent tried to offer a reason why they looked radically different than in the TOS episodes. STD has thrown that reasoning away and offered no explination as to why. Oh, they did give them hair and beards this season, though, so they retconned their own Klingons in that regard. They also changed a lot of the Klingon traits, especially how they hold "honor" above all else. They just seem unnecessarily savage. I still blame Game of Thrones for its influence on the first season of STD (or rather the execs who wanted to make Trek into GoT).
By the way, the fact that Ash Tyler/Voq is an official member of Section 31, and thereby an official member of Starfleet, doesn't that mean Worf is no longer the first Klingon in Starfleet? I guess they can say Ash's Klingon-ness is a secret to most, so it doesn't really count.
Spock - Obviously a HUGE retcon to his character. Now he has a human foster sister that he grew up with and shaped his character, yet we never heard of her before STD. By the way, where was Sybok in all this? Wasn't Spock's half brother raised in the family too? ST V was a crap film, but it's still cannon as far as I know (I hated the retcon of Sybok then, as I do the adding of Michael Burnham to Sarek's clan).
Saru - He, and his race, get a retcon this season too. Now he's not the fearful, death-smelling alien he once was, but a confident killing machine. Not sure what to make of this, other than maybe the production crew didn't want to have to CGI those danged ganglia in all the time. Seriously though, they probably realized it doesn't serve much in storytelling to have a character who constantly has a physical reaction to danger.
Enterprise - Captain Pike gets reassigned to Captain the USS Discovery, which I don't believe was ever established before. There's oviously a lot of retconned stuff regarding the technology of TOS and Pike's Enterprise, but I take some of it with a grain of salt. I do think there's a way to upgrade the visuals and tech of the TOS era in moderation without going full 21st century sci-fi future tech visuals. Which leads me to the tech in STD...
Technology - So now we have the spore drive, enabling instantaneous access to anywhere in the universe (which kind of invalidates TOS's Five Year Mission "to boldly go where no man has gone before"). I will say that Star Trek hasn't always seemed consistent about the speed at which their ships can travel and how long (or short) it can take for a starship to get to any place in the universe (it seemed like earth was always just a few hours away, no matter where any of the ships were - except Voyager, of course).
You also have Section 31 creating a personal time travel suit, using time crystals (ugh), and other technology like communicator badges well before the TNG era. The tech of the com badges don't bother me as much, since we actually have the technology to do that now, in real life. It only bothers me that they made it a bigger deal by pointing out how Section 31 has those cool communicator badges wile Discovery and the rest of the fleet doesn't. It doesn't really serve any purpose in storytelling, and they've offered no reason as to why it really matters.
I'm sure there's more retconned stuff to get into, but I'm tired of typing for now.
