Raspberry Pi OS (Debian) bullseye is now available for testing. I’ve taken the plunge on my emonpi because it also runs home assistant, which requires a newer python for the latest releases (and keeping my local changes was fragile at best, anyway I digress…).
The upgrade broke a couple of things. PHP 7.4 is now the default, so you have to tell it that your mysql instance is available in /home/pi/data/mysql/mysql.sock, not in /tmp, by editing both /etc/php/7.4/{apache2,cli}/php.ini. If you use it, you need to uninstall the old mosquitto plugin and then pecl install Mosquitto-alpha and phpenmod mosquitto.
The new packages come with new config files, so you have to be careful to update the new files with the changes required for emonpi. For example, mysql will want to delete the conf line which puts the mysql socket in /home/pi/data. If you use mosquitto, mosquitto.conf removes some critical lines too.