I would not decanonize any series, or any episodes. Even when I put DIS, the majority of ST, some episodes of SNW, S31, SFA, and Very Short Treks into an alternate reality that’s completely separate from the Prime timeline and Kelvin timeline. I still consider all of that canon too. IDIC and all that.
But I do have a list of things within episodes or series that should go:
Decanonize the Chardybis mission and the whole dating of the 52 stars on the US flag. The original script for “The Royale” suggest the flag was in use between 2053 and 2079, and the Charybdis was launch was in 2067. While the actual episode places both originating in 2037. So, retcon both the flag and the mission to the original script dates for both the flag and the mission being a post-atomic horror thing. It would align with the final act of “The Sehlat Who Ate Its Tail” much better, since the flag on that Earth ship only used 50 stars.
Decanonize the idea that Romulus does not exist in the 25th century or beyond. Just use a Genesis device and make a new Romulus already!
Decanonize Andy Dick ...the synth ban already gives a great cover as to why that particular EMH model is no longer around.
Decaonize the decommissioning of the Ent-F, and the Titan-A being rechristened the Ent-G. The Ent-F had another decade in her, and its kind of unsettling that these starships are so disposable now and are only good for about a decade and a bit, when the OG USS Enterprise lasted 40 years. And as for the Ent-G, I'm fine with Seven of Nine being her captain...just why that ship as the Ent-G?