I would like to add the short day before the Start Date in my form. EG ‘wo 28-12-2023’ Here a screenshot

This is my form code for this field:
<div class="form-group">
<label for="start_date">Start Date</label>
<input type="date" class="form-control form-control-sm small-size" id="start_date" name="start_date"
value="{{ shift.start_date|date:'Y-m-d' }}">
</div>
The format given here can not be changed. Probably because it is the way the date is stored in the database. The european date is shown correct in the form. This format is set in the settings.py:
LANGUAGE_CODE = 'nl-NL'
TIME_ZONE = 'Europe/Amsterdam'
USE_I18N = True
USE_TZ = True
Is it possible to show this day letters ‘wo 28-12-2022’ and still just input ‘28-12-2022’?
Within that specific input field, no. HTML doesn’t provide for any “not-to-be-submitted-data” within an input field.
You’d have to do something like what Django Crispy Forms refers to as “PrependedText”.
Note: I am not saying that you need to use Crispy - only that what they do for this situation is what you’re looking to do, and you could examine that code to see how they do it. That might provide you with some ideas.
Side note:
This is not an accurate statement. It’s a characteristic of the input type="date"
element in the browser. See the blue note box at <input type="date"> - HTML: HyperText Markup Language | MDN
I solved it like this:

<div class="form-group">
<label for="start_date">Start Date / {{ shift.start_date|date:'l' }}</label>
<input type="date" class="form-control form-control-sm small-size" id="start_date" name="start_date"
value="{{ shift.start_date|date:'Y-m-d' }}">
</div>