There is a simple way to do the same, please add this code snippet to functions.php of the current theme.
function add_avif_to_upload_mimes($mime_types) { $mime_types['avif'] = ‘image/avif’; $mime_types['avifs'] = ‘image/avif-sequence’; return $mime_types; } add_filter(‘upload_mimes’, ‘add_avif_to_upload_mimes’);
if not work, then try
https://wordpress.org/plugins/mime-types-plus/