Register custom Gutenberg block category

custom-gut-category.php

<?php
function new_category( $categories, $post ) {
	return array_merge(
		$categories,
		array(
			array(
				'slug' => 'custom-category',
				'title' => __( 'Custom Category', 'language' ),
			),
		)
	);
}
add_filter( 'block_categories', 'new_category', 10, 2);

remove-core-blocks.php

<?php
add_filter( 'allowed_block_types', 'allowed_block_types' );
 
function allowed_block_types( $allowed_blocks ) {
 
	return [
		'core/image',
		'core/paragraph',
		'core/heading'
	];
 
}