This.
I cannot imagine a single reason why a new shooter would consider a Glock 23. While its true you can get aftermarket 9x19 barrels, I just dont see that as a good argument for a new shooter in choosing a handgun. I don't even see it as a good argument for an experienced shooter.
While the .40 S&W isn't dead or obsolete, it most certainly is becoming an albatross along with .357sig and .45GAP. Not because those cartridges are inferior, but because sales of .40 are abysmal compared to 9x19. Lack of sales of .40 pistols impacts the ammunition market and less demand means higher prices for those cartridges.
A new shooter should be putting as many rounds downrange as they can afford, and thats easier to do with 9x19. There is a reason the FBI, Secret Service and others went back to 9x19.