Symfony DateTime format errors - datatransformation (external datepicker)

Question

I'm working with Symfony 6 and a TempusDomini datepicker. I have read (amongst many others) the symfony documentation, https://symfony.com/doc/current/reference/forms/types/datetime.html. Based on the documentation I found I initially implemented the form builder as followed:

->add('TextDateField')
->add('RegistrationDateTime', DateTimeType::class, [
                'required' => false,
                'widget' => 'single_text',
                'format' => 'm/d/Y, h:i a',
                'attr' => [
                    'class' => 'datetimepicker-input',
                    'data-target' => '#datetimepicker1'
                ],
                'html5' => false,
            ])
        

The "TextDateField" is for troubleshooting, see explanation below. And the actual TWIG file looks like this (for the TextDateField I have a similar datapicker block as the one for RegistrationDateTime):

{{form_start(form)}}
{{form_row(form.username)}}

                <div class> 
                    <label for="datetimepicker1Input" class="form-label">Simple picker</label>
                    <div class="input-group" id="datetimepicker1" data-td-target-input="nearest" data-td-target-toggle="nearest">
                        <input id="user_creation_form_RegistrationDateTime" name="user_creation_form[RegistrationDateTime]" type="text" class="form-control" data-td-target="#datetimepicker1">
                        <span class="input-group-text" data-td-target="#datetimepicker1" data-td-toggle="datetimepicker">
               <span class="fa-solid fa-calendar"></span> 
             </span>
 
                </div>
                <script type="text/javascript">
                    const picker = new tempusDominus.TempusDominus(document.getElementById('datetimepicker1'));
                </script>
             </div>
 
{{form_row(form.roles)}}
{{form_row(form._token)}}
{{form_row(form.submit)}}

What I notice is that the dates are correctly given from a datepicker to the controller if passed via Text. Please see this dump where you can see 2 datepicker values as passed to the controller, both for the same dates (6 may 2022)

App\Entity\TUser^ {#361
  -id: null
  -username: "scdsqd"
  -roles: array:2 [
    0 => "ROLE_USER"
    1 => "ROLE_ADMIN"
  ]
  -TextDateField: "05/06/2022, 12:42 PM"
  -RegistrationDateTime: DateTime @1640599500 {#828
    date: 2021-12-27 11:05:00.0 Europe/Berlin (+01:00)
  }
}

So as you can see the text is passed correctly for the "text" datepicker but using the symfony DateTimeType::class messes it up by giving a seemingly random date. Using other formats as datetime (for example timestamp) is not possible.

So how can I pass the value correctly to the database?

One possible "solution" is to work with TextType::class but since I want to keep the field RegistrationDateTime in the database as a DateTimeType this is not the best solution either since that would mean I have to transform the data.

Maybe I'm not looking at the right place, but it seems to me as if Symfony is not well adjusted to use external datepickers. I have found tons of post with people struggling to implement a datepicker...

Is the approach I use correct?

How can I "force" symfony to "understand" the datepicker provided dates?

If the only way is to use TextType in the form-builder, how do I tackle the datatransformations to make sure that via doctrine I save in the datetime format?

Any pointers in the right direction are welcome... I'm getting rather frustrated by it since I've struggled on it an embarrassingly long time now...