Whitelist Author of Private Post

You can use the post_password_required filter.

function wpse406803_whitelist_author( $required, $post ) {
    
    //Check if current user is the post author
    if ( $post->post_author == get_current_user_id() ) {
        return false;
    }
    
}
add_filter( 'post_password_required', 'wpse406803_whitelist_author', 10, 2 );