Default content overwrittern when using a default post format

[Chouby]

1. Programmatically define a default content. For example:

   <?php
   add_filter(
           'default_content',
           function() {
                   return 'My default content';
           }
   );
   

2. Go to Settings > Writing and select a default post format, for example, 'image'.
3. Create a new post.

I expect the editor content to display "My default content'. It displays a block image instead.

The test must be done ith a theme supporting post formats such as Twenty Twenty One.