add-arg.php

<?php
add_action( 'rest_endpoints', function( $endpoints ){

	if( isset( $endpoints[ 'wp/v2/posts' ] ) ){
		foreach( $endpoints[ 'wp/v2/posts' ] as &$post_endpoint ){
			if( 'GET' == $post_endpoint[ 'METHOD' ] ){
				$post_endpoint[ 'args' ][ 'type' ] = array(
					'description' => 'Post types',
					'type' => 'array',
					'required' => false,
					'default' => 'post'
				);
			}
		}
	}
	return $endpoints;
}, 15 );

filter-wp-query-2.php

<?php
add_action( 'rest_post_query', function( $args, $request ){
	$post_types = $request->get_param( 'type' );
	if( ! empty( $post_types ) ){
		if( is_string( $post_types ) ){
			$post_types = array( $post_types );
			foreach ( $post_types as $i => $post_type ){
				$object=  get_post_type_object( $post_type );
				if( ! $object || ! $object->show_in_rest   ){
					unset( $post_types[ $i ] );
				}
			}
		}
		$args[ 'post_type' ] = $post_types;
	}
	return $args;
}, 10, 2 );

filter-wp-query.php

<?php
add_action( 'rest_post_query', function( $args, $request ){
	$post_types = $request->get_param( 'type' );
	if( ! empty( $post_types ) ){
		if( is_string( $post_types ) ){
			$post_types = array( $post_types );
			foreach ( $post_types as $i => $post_type ){
				$object=  get_post_type_object( $post_type );
				if( ! $object || ! $object->show_in_rest   ){
					unset( $post_types[ $i ] );
				}
			}


		}
		$post_types[] = $args[ 'post_type' ];
		$args[ 'post_type' ] = $post_types;
	}
	return $args;
}, 10, 2 );

remove-user-endpoints.php

<?php
add_action( 'rest_endpoints', function( $endpoints) {
	foreach ( $endpoints as $endpoint => $args ){
		if( false !== strpos( '/wp/v2/users', $endpoint ) ){
			unset( $endpoints[ $endpoint ]  );
		}
	}
	return $endpoints;
});

type-check.php

<?php
/** @var WP_REST_Request $request */
$type = $request->get_param( 'type' );