The message isn’t as bad because it didn’t carry out any update on the database and data itself. So you can still do a backup:
- save
data/andconfig/-folder - save database (see in the
config/config.phpwhich type of database and the associated credentials, for sqlite it’s just a file in thedata/-folder)
Here is a guide on what to do: Updates between multiple major versions and downgrades are unsupported
The current version you have installed should be shown in config/config.php. And the version you accidentally tried to upgrade is in the file version.php.