Not the most pleasant experience.. I expected a smoother upgrade from Debian team. Upgrading from 8 to 9 was a walk in the park compared to this.
1. MySQL silently fails to start after upgrade
MySQL was left behind at version 5.5 after upgrade and would just not start anymore, probably segfaulting. There is no mysql-server package anymore so I had really no other option but to remove it and install mariadb. In addition, I had trouble running mariadb due to requirement to run mysql_upgrade .. but I couldn't run that because I had no working instance of mysql server running! Installing package default-mysql-server instead somehow solved the problem.
2. phpMyAdmin removed from packages
Not sure how maintaining phpMyAdmin is such a big task that the package was dropped from repos. Regular setup is simply unzipping the code and add an apache config.
3. docker fails due to nftables switch
Docker is such a big and important package these days… and breaks due to iptables no longer being the default. I would expect the upgrade process to not do the switch in this case.
4. apt autoremove anomaly
For some reason running autoremove wanted to purge essential packages such as php, gcc and python3. I did not pay too much attention but alerts started going off when ifup was getting removed and my ssh connection was lost. ?????????? (10 question marks)
Luckily this was all of the troubles, dealing with broken wordpress plugins was a relaxing task afterwards.