@ExTexan,
Thanks for the code and the explanation, can you please enlighten with more detail on
{% set params = _context.email.params.legacy_message.params %}
Usage of this above and how are you sending email now.
My understanding is you have used this above set parms in the Twig you were already using but not just have renamed them or changed the 'swiftmailer' prefix to 'email' to accommodate the new change.
How ever I am not sure which mechanism are you using to send the emails now and also where have you printed this $email = {Drupal\symfony_mailer\Email}
Please help, thanks.
This is a duplicate of this and also as mentioned, D10 support has been added in 4.0 Version of the module, so closing it.
https://www.drupal.org/project/cshs/issues/3296907 →
I am adding the patch which support Drupal coding standards as well in addition to comment number 18.