Index: src/wp-admin/includes/post.php
===================================================================
--- src/wp-admin/includes/post.php	(revision 43867)
+++ src/wp-admin/includes/post.php	(working copy)
@@ -1882,6 +1882,7 @@
  *
  * @param int|WP_Post $post Post ID or WP_Post object.
  * @return bool Whether the post can be edited in the block editor.
+ * @deprecated 5.0.0-beta4 Use `use_block_editor` instead.
  */
 function use_block_editor_for_post( $post ) {
 	$post = get_post( $post );
@@ -1896,7 +1897,7 @@
 		return false;
 	}
 
-	$use_block_editor = use_block_editor_for_post_type( $post->post_type );
+	$use_block_editor = use_block_editor( $post );
 
 	/**
 	 * Filter whether a post is able to be edited in the block editor.
@@ -1905,11 +1906,46 @@
 	 *
 	 * @param bool    $use_block_editor Whether the post can be edited or not.
 	 * @param WP_Post $post             The post being checked.
+	 * @deprecated    5.0.0-beta4       Use `use_block_editor` instead or `use_block_editor_for_{$post_type}` to filter a specific post type.
 	 */
 	return apply_filters( 'use_block_editor_for_post', $use_block_editor, $post );
 }
 
 /**
+ * Return if the block editor should be used or not.
+ *
+ * @since 5.0.0
+ *
+ * @param int|WP_Post $post Post ID or WP_Post object.
+ * @return bool Whether the post can be edited in the block editor.
+ */
+function use_block_editor( $post = null ) {
+	$post = get_post( $post );
+
+	if ( ! $post ) {
+		return false;
+	}
+
+	// We're in the meta box loader, so don't use the block editor.
+	if ( isset( $_GET['meta-box-loader'] ) ) {
+		check_admin_referer( 'meta-box-loader' );
+		return false;
+	}
+
+	$use_block_editor = use_block_editor_for_post_type( $post->post_type );
+
+	/**
+	 * Filter whether a post is able to be edited in the block editor.
+	 *
+	 * @since 5.0.0
+	 *
+	 * @param bool    $use_block_editor Whether the post can be edited or not.
+	 * @param WP_Post $post             The post being checked.
+	 */
+	return apply_filters( 'use_block_editor', $use_block_editor, $post );
+}
+
+/**
  * Return whether a post type is compatible with the block editor.
  *
  * The block editor depends on the REST API, and if the post type is not shown in the
@@ -1941,8 +1977,11 @@
 	 *
 	 * @param bool   $use_block_editor  Whether the post type can be edited or not. Default true.
 	 * @param string $post_type         The post type being checked.
+	 * @deprecated   5.0.0-beta4        Use `use_block_editor_for_{$post_type}` instead.
 	 */
-	return apply_filters( 'use_block_editor_for_post_type', true, $post_type );
+	$deprecated = apply_filters( 'use_block_editor_for_post_type', true, $post_type );
+
+	return apply_filters( "use_block_editor_for_{$post_type}", $deprecated );
 }
 
 /**