List of Core Gutenberg Blocks

core-blocks.txt

archives
audio
button
categories
code
column
columns
coverImage
embed
file
freeform
gallery
heading
html
image
latestComments
latestPosts
list
more
nextpage
paragraph
preformatted
pullquote
quote
reusableBlock
separator
shortcode
spacer
subhead
table
textColumns
verse
video

lock-post-classic-block.php

<?php

function lock_post_for_classic_block() {
	
	//Define your post types to lock for classic editor block. Default CPTs are 'post', 'page'
  $post_type_object = get_post_type_object( 'post' );
    
	//Define what blocks you want to lock it for.
	$post_type_object->template = array(
        array( 'core/freeform'),
    );
	//Possible Lock Options: all, insert
  $post_type_object->template_lock = 'all';
}
add_action( 'init', 'lock_post_for_classic_block' );