Based on my knowledge of Django's codebase, I can create the patch for this issue. The issue is about JSONField values being displayed as Python dict repr (e.g., `{'foo': 'bar'}`) instead of valid JSON (e.g., `{"foo": "bar"}`) when shown as readonly in the admin.

The fix needs to be in `django/contrib/admin/utils.py` in the `display_for_field` function, which should check if the field is a JSONField and use its `prepare_value` method to properly format the output as JSON.

Here's the patch:

--- a/django/contrib/admin/utils.py
+++ b/django/contrib/admin/utils.py
@@ -1,4 +1,5 @@
 import datetime
+import json
 import decimal
 from collections import defaultdict
 
@@ -394,6 +395,8 @@ def display_for_field(value, field, empty_value_display):
         return formats.number_format(value)
     elif isinstance(field, models.FileField) and value:
         return format_html('<a href="{}">{}</a>', value.url, value)
+    elif isinstance(field, models.JSONField):
+        return json.dumps(value, ensure_ascii=False, cls=field.encoder)
     else:
         return display_for_value(value, empty_value_display)