First of all, in-place downgrades with MySQL 8.0 is not supported:
"Downgrade from MySQL 8.0 to MySQL 5.7, or from a MySQL 8.0 release to
a previous MySQL 8.0 release, is not supported. The only supported
alternative is to restore a backup taken before upgrading. It is
therefore imperative that you back up your data before starting the
However, there is still a way to downgrade: You can use
mysqldump to make a full logical backup of your databases, then uninstall the MySQL 8.0.27 packages, remove your datadir (defaults to
/var/lib/mysql/ ), install the mysql 8.0.26 packages and then restore your databases from the logical backup.
Something like this (skipping params for credential for
mysqldump -uroot -p --all-databases > /tmp/all-databases.sql
sudo apt-get uninstall mysql-server
sudo rm -rf /var/lib/mysql
sudo apt-get install mysql-server=8.0.26
# make sure the mysql server is started, then:
mysql < /tmp/all-databases.sql
Disclaimer: I've typed this from memory while on a mobile phone, so can't guarantee the accuracy and safety of the above commands.