if you return empty it will break

was this variable also removed ?

Yes, it was removed in MariaDB 10.10 : https://mariadb.com/docs/server/server-usage/storage-engines/innodb/innodb-system-variables

Would you mind refactoring this so we have a clear path that the two variables are only displayed and fetched if the database version is the right one ?
Like you did in the other PR

I just noticed that even in MySQL this variable is quite useless:
https://dev.mysql.com/doc/refman/8.4/en/innodb-parameters.html#sysvar_innodb_version

Maybe it's better to remove it completely?

It depends if it useless since before the minimum MySQL version for phpMyAdmin or not
They say we can use @@version instead

OK, then we can juste replace :

return $dbi->fetchValue('SELECT @@innodb_version;') ?: '';

With:

return $dbi->fetchValue('SELECT @@version;') ?: '';

Probably yes, but it needs to be checked on the lowest version supported

If you just replace it then it becomes useless, right? I think the point was to check whether this setting exists and is not empty.

I think that the function getInnodbPluginVersion() is useless, since it is only used in libraries/classes/Operations.php as follows:

        $innodbPluginVersion = $innodbEnginePlugin->getInnodbPluginVersion();
        $innodb_file_format = '';
        if (! empty($innodbPluginVersion)) {
            $innodb_file_format = $innodbEnginePlugin->getInnodbFileFormat() ?? '';
        }

This block could just be replaced by:

$innodb_file_format = $innodbEnginePlugin->getInnodbFileFormat() ?? '';

And the function getInnodbFileFormat() could be optimized as:

    public function getInnodbFileFormat(): ?string
    {
        global $dbi;

        return (
          ($dbi->isMariaDB() && $dbi->getVersion() >= 100600)
          || ($dbi->isMySql() && $dbi->getVersion() >= 80000) 
        ) ? '' : $dbi->fetchValue("SELECT @@innodb_file_format;");
    }

Indeed, please apply this