Been a while since I've used Debian but I'm sure Debian is already using NetworkManager. This means the Raspberry OS has actually removed NetworkManager from its Debian base and put in something else. I agree with the OP this shouldn't happen. For my Raspberry Pi, I ended up switching out the Raspberry Pi OS' default networking manager thingy in preference for NetworkManager so I could share wireless networking configuration among my devices. It also helps with troubleshooting as well since I can just use the same commands I use on other Linux machines even those running other distros.