Steps to reproduce the issue

Right now we can inject a custom form into preprocessForm with onContentPrepareForm event from a plugin group.

Issue is when trying to save the form it does not inject the plugin group name into preprocessForm and the controller validation remove the custom data entered into the form data.

This line should be extended with the plugin group value of the preprocessForm function. As right now it will always load the 'content' group and there is no way to override it.

Expected result

Be able to load plugin group for preprocessForm on save.

Actual result

Not possible.

System information (as much as possible)

Joomla 4.2

Additional comments

Maybe add an $options['group'] as the would be hard to extend the loadForm function with a new parameter.

Example:
$this->preprocessForm($form, $data, $options['group']);