well we all know now police were unable to enter the building until the proper person with the proper key showed up, the door was only propped open for the shooter, police in Uvalde apparently were never trained to break down doors or break glass
I think I saw or read a news story stating that the doors were made of steel and open outward. If so, that would make them hard to breach without using some serious explosives.
That said, I also heard that they had to wait for someone to show up with a key, so why don't they have easier access to keys?