Comment 12 for bug 1914636

It'd be hard to fix postinst files already on the system to properly deal with the removal of /etc/mysql, but presumably going forward it might be possible to make all the inst scripts not assume its existence.

That there may also be similar issues relating to upgrade from mysql-5.7 to mysql-8.0 is unsurprising, but reading comment #5 onward that seems to me like a separate issue that deserves its own bug report. This report would better focus on the original issue caused by the removal of /etc/mysql.