Update to 20.0.9 instead of 21.0.1

Nextcloud version (eg, 20.0.5): 20.0.8
Operating system and version (eg, Ubuntu 20.04): hosted webspace Debian GNU/Linux 8 (jessie)
Apache or nginx version (eg, Apache 2.4.25): Apache 2
PHP version (eg, 7.4): 7.4.3

The issue you are facing:
My provider is running mysql Ver 14.14 Distrib 5.7.18, for Linux (x86_64) using EditLine wrapper only, so I’m stuck to NC20 for now.

According to admin > overview I can upate to 20.0.9 (“stable” channel). If I click on the button to open the updater, it says

Initializing

Current version is 20.0.8.
Update to Nextcloud 21.0.1 available. (channel: “stable”)
Following file will be downloaded automatically: https://download.nextcloud.com/server/releases/nextcloud-21.0.1.zip

Because I read in admin > overview that 20.0.9 is available I simply clicked “Continue Update”… and had to restore my NC 20.0.8 instance.

Checking in Terminal:
$ php7.2 updater/update.phar
[…] Update to Nextcloud 20.0.9 available. (channel: “stable”) […]

$ php7.4 updater/update.phar
[…] Update to Nextcloud 21.0.1 available. (channel: “stable”) […]

How can I update to 20.0.9 using the webupdater?

Is this the first time you’ve seen this error? (Y/N): N

Steps to replicate it:

  1. as describe above

The output of your Nextcloud log in Admin > Logging:
only some

Error	PHP	Directive 'safe_mode_protected_env_vars' is no longer available in PHP 5.4 or newer at Unknown#0

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

$CONFIG = array (
  'instanceid' => 'random',
  'passwordsalt' => 'random',
  'secret' => 'random',
  'trusted_domains' =>
  array (
    0 => 'my.domain.de',
  ),
  'datadirectory' => '/var/www/webuser/html/nextcloud-data',
  'dbtype' => 'mysql',
  'version' => '20.0.8.1',
  'overwrite.cli.url' => 'https://my.domain.de',
  'allow_local_remote_servers' => true,
  'dbname' => 'usr_webuser_3',
  'dbhost' => '127.0.0.1',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'webuser',
  'dbpassword' => 'secret',
  'installed' => true,
  'mail_smtpmode' => 'smtp',
  'mail_smtpsecure' => 'ssl',
  'mail_sendmailmode' => 'smtp',
  'mail_from_address' => 'Administrator',
  'mail_domain' => 'my.domain.de',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_smtphost' => 'my.provider.de',
  'mail_smtpport' => '465',
  'mail_smtpname' => 'webusersmtp',
  'mail_smtppassword' => 'secret',
  'maintenance' => false,
  'theme' => '',
  'loglevel' => 2,
  'enable_previews' => true,
  'updater.release.channel' => 'stable',
  'updater.secret' => 'random',
);

The output of your Apache/nginx/system log in /var/log/____:

n/a