Module config not saved, "Password reset form email address only description cannot be longer than 128 characters …"

I'm unable to reproduce this issue. can you test it in a fresh installation?

I tested the issue on several fresh and clean installs — with german locale, issue is always occuring.
Just use this DDEV recipe:

mkdir testsite-german && cd testsite-german
ddev config --project-type=drupal10 --docroot=web
ddev start
ddev composer create drupal/recommended-project:^10
ddev composer require drush/drush
ddev drush site:install --account-name=admin --account-pass=admin --locale=de -y
ddev launch
ddev composer require 'drupal/mail_login:^4.0'
ddev drush pm:enable mail_login  
ddev launch $(ddev drush uli)

Same problem for me, also german locale.

What I noticed: The field from the error edit-mail-login-password-reset-email-only-description is set to display:none, I don't know why. Seems that the german translation for the field is too long, but since we can not see the field, we can not fix it via the UI.

When I manually show the field, the error says: Password reset form email address only description cannot be longer than 128 characters but is currently 132 characters long.

Same thing for Spanish.

How I solved it:

- Search in the inspector (F12) the input field edit-mail-login-password-reset-email-only-description.
- Change its value to a shorter message, you can achieve this by double clicking on the value attribute of the element.
- Click on Save configuration, it should not prompt the same error again.

I tried workaround described by mike gp, comment #5. Unfortunately, for me it didn't work, still couldn't save the configuration.
I located this HTML in web developer:

<input
  data-drupal-selector="edit-mail-login-password-reset-email-only-description"
  aria-describedby="edit-mail-login-password-reset-email-only-description--description"
  type="text"
  id="edit-mail-login-password-reset-email-only-description"
  name="mail_login_password_reset_email_only_description"
  value="My new shorter value"
  size="60"
  maxlength="128"
  class="form-text form-element form-element--type-text form-element--api-textfield"
  data-drupal-states='{"required":{":input[name=\u0022mail_login_email_only\u0022]":{"checked":true,"visible":true}},"visible":{":input[name=\u0022mail_login_override_login_labels\u0022]":{"checked":true,"visible":true},":input[name=\u0022mail_login_email_only\u0022]":{"checked":true}}}'
  data-once="states"
  required="required"
/>

And changed original value to "My new shorter value".
Any help making workaround actually working is much appreciated.
Or, even more appreciated is a proper fix for the issue!

Fixed in 4.2.2 and 3.2.1