How to enable post images and remove default generated image sizes in WordPress.

Load-post.php

<?php

// Post formats
add_theme_support('post-formats', ['aside', 'image', 'video', 'quote', 'link', 'gallery', 'status', 'audio', 'chat']);

// Enable post thumbnails
add_theme_support('post-thumbnails');

// Update default thumbnails size (post-thumbnail, medium_large)
set_post_thumbnail_size(1280, 720, true);
add_image_size('medium_large', 768, 480, true);

// Add thumbnail custom sizes
add_image_size('post-thumbnail-large', 1280, 720, true);
add_image_size('post-thumbnail-medium', 640, 360, true);
add_image_size('post-thumbnail-small', 360, 200, true);

// Remove thumbnails
function remove_extra_image_sizes() {
    foreach (get_intermediate_image_sizes() as $size) {
        if (!in_array($size, array('medium_large', 'post-thumbnail', 'post-thumbnail-large', 'post-thumbnail-medium', 'post-thumbnail-small'))) {
            remove_image_size( $size );
        }
    }

    // Remove default thumbnails
    update_option('thumbnail_size_h', 0);
    update_option('thumbnail_size_w', 0);
    update_option('medium_size_h', 0);
    update_option('medium_size_w', 0);
    update_option('medium_large_size_w', 0);
    update_option('medium_large_size_h', 0);
    update_option('large_size_h', 0);
    update_option('large_size_w', 0);
}

// Add and next regenerate images with wp plugin
add_action('init', 'remove_extra_image_sizes');

?>