Simplenews: Error: Call to a member function getMail()

Problem/Motivation

Sending eMail from the simplenews subscription block results in

1:
Notice: Undefined variable: params in Drupal\symfony_mailer_bc\Plugin\EmailBuilder\SimplenewsEmailBuilder->fromArray() (Zeile 49 in /var/www/vhosts/mysite.com/httpdocs/web/modules/contrib/symfony_mailer/modules/symfony_mailer_bc/src/Plugin/EmailBuilder/SimplenewsEmailBuilder.php)
2:
Notice: Trying to access array offset on value of type null in Drupal\symfony_mailer_bc\Plugin\EmailBuilder\SimplenewsEmailBuilder->fromArray() (Zeile 49 in /var/www/vhosts/mysite.com/httpdocs/web/modules/contrib/symfony_mailer/modules/symfony_mailer_bc/src/Plugin/EmailBuilder/SimplenewsEmailBuilder.php)
3:
Error: Call to a member function getMail() on null in Drupal\symfony_mailer_bc\Plugin\EmailBuilder\SimplenewsEmailBuilderBase->build() (Zeile 25 in /var/www/vhosts/dorfladen-bierbergen.com/httpdocs/web/modules/contrib/symfony_mailer/modules/symfony_mailer_bc/src/Plugin/EmailBuilder/SimplenewsEmailBuilderBase.php)

ending up with
The website encountered an unexpected error. Please try again later.

Steps to reproduce

Drupal core 9.3.13
Simplenews all newer versions

Proposed resolution

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