Django admin - using autocomplete and filter on choices fields (not ManyToMany or ForeignKey)

This is my model:

class Academic(models.Model):

SCHOOL_COLLEGE_SERVICE = [
    ('School Of Humanities', 'School Of Humanities'),
    ('School Of Culture & Creative Arts', 'School Of Culture & Creative Arts'),
    ('School Of Modern Languages & Cultures', 'School Of Modern Languages & Cultures'),
    ('School Of Critical Studies', 'School Of Critical Studies'),
    ('Arts  College Of Arts Administration', 'Arts  College Of Arts Administration'),
    ]

school = models.CharField(choices=SCHOOL_COLLEGE_SERVICE, max_length=50, blank=True, null=True)

I'd like to have a nice autocomplete / filter in my Django administration interface. Unfortunately it seems that it is not possible to have autocomplete if the dataset doesn't come from a ManyToMany or ForeignKey relationship. This is what I tried:

from django.contrib import admin
from .models import Academic, Partner, Project
from admin_auto_filters.filters import AutocompleteFilter
import django_filters

@admin.register(Academic)
class AcademicAdmin(admin.ModelAdmin):
    search_fields = ['surname', 'forename']
    #school = django_filters.ChoiceFilter(choices=Academic.SCHOOL_COLLEGE_SERVICE)
    #autocomplete_fields = ['school']

I know I can also set a queryset like so:

class SchoolFilter(django_filters.FilterSet):
    class Meta:
        model = Academic
        fields = ['school',]

But Django still complains that The value of 'autocomplete_fields[0]' must be a foreign key or a many-to-many field. How can I achieve what I want?

if you don't want to rely on third party libraries, here is a simple widget that reuses Django's autocomplete media files (select2):

class AdminAutocompleteSelectWidget(forms.Select):
    def __init__(self, choices=(), attrs=None):
        super().__init__(attrs)
        self.choices = choices

    def render(self, name, value, attrs=None, renderer=None):
        select_html = super().render(name, value, attrs, renderer)
        select2_script = f"""
        <script type="text/javascript">
            (function($) {{
                $(document).ready(function() {{
                    $('#id_{name}').select2();
                }});
            }})(django.jQuery);
        </script>
        """
        return select_html + select2_script

    @property
    def media(self):
        # Reuse the AutocompleteMixin's media files
        return AutocompleteMixin(None, None).media