You say "same universe" as Diggle even though Diggle is Arrowverse Earth-1 and Supergirl/Superman were from Earth-38 up until Crisis, which unfortunately due to the pandemic, resulted in not much crossover. After the events of Crisis, Superman (now living on Earth Prime) is on the phone with Lois and is surprised at Lois mentioning the twins instead of the one baby they just had. On top of that, S&L has them as teens and clearly not 15 years in the future, so it's not post-crisis Earth-Prime that merged at least Earth-1 and Earth-38, while still clearly leaving the realities of Titans, Doom Patrol, and S&L separate.