How to upgrade Raspberry Pi OS from Buster to Bullseye

sudo apt update 
sudo apt dist-upgrade -y
sudo rpi-update


sudo apt remove libc6-dev
sudo sed 's/buster/bullseye/g' /etc/apt/sources.list
sudo sed 's/buster/bullseye/g' /etc/apt/sources.list.d/raspi.list

sudo apt update
sudo apt install libgcc-8-dev 
sudo apt install gcc-8-base
sudo apt dist-upgrade
sudo apt autoclean

change /lib/dhcpcd5/dhcpcd to /usr/sbin/dhcpcd in /etc/systemd/system/dhcpcd.service.d/wait.conf

https://tech.utzer.de/2023/05/11/upgrade-raspberry-pi-raspbian-from-buster-to-bullseye/
https://www.tomshardware.com/how-to/upgrade-raspberry-pi-os-to-bullseye-from-buster