It seems that heic images are increasingly popular way to store images (the default image format since ios 11, but browsers do not support them. Site visitors may attempt to upload an heic image from their phone to an image field, but the default file extension validation prevents that. If a site admin allows heic file extension for the field then the file can get uploaded, but is not displayed as an image because browsers don't support heic.
Drupal 7 has the Auto Upload Convert module which is not super popular, but attempts to solve this problem.
For Drupal 9+ I can't find a module or answer about how to solve the problem.