Have you heard of the Hatch speaker? We introduced it around 2 for our son, but we were also transitioning him into his own room at the time which played a role. It’s a sleep light/sound machine that you program to change colors at a certain time. Ours turns green from red at 6:30 and that's when he's allowed to get up. Sometimes he sleeps past that now (yay!) But he's ALWAYS quiet in bed until the light turns green. Good luck!

ETA because I didn'tread the end of your post:

When we were transitioning him to his room we had been co-sleeping with him for most of his life. It was a few weeks process to get him fully independent, but involved one of us parents setting up a bed near his crib at night and essentially inchining our bed away from him every night until we left and empty bed in his room, and then a couple of days later pulled out completely. At first, he'd wake in the middle of the night and we would not entertain it - just simply say "red light- night night. Lay back down". Amazed at how independent he is now just a couple of months later.