function allowed_blocks( $allowed, $context ) {
    // Site Editor usually edits these post types.
    if ( isset( $context->post ) && $context->post ) {
        $post_type = $context->post->post_type;

        // Allow all blocks in the Site Editor.
        if ( in_array( $post_type, array( 'wp_template', 'wp_template_part' ), true ) ) {
            return true;
        }

        // Restrict blocks for regular content.
        if ( in_array( $post_type, array( 'post', 'page' ), true ) ) {
            return array(
                'core/paragraph',
                'core/heading',
                'core/image',
            );
        }
    }

    // Fallback: detect the Site Editor screen directly if available.
    if ( function_exists( 'get_current_screen' ) ) {
        $screen = get_current_screen();
        if ( $screen && 'site-editor' === $screen->id ) {
            return true;
        }
    }

    // Another fallback: some contexts expose a name like 'core/edit-site'.
    if ( isset( $context->name ) && 'core/edit-site' === $context->name ) {
        return true;
    }

    return $allowed;
}

add_filter( 'allowed_block_types_all', 'allowed_blocks', 10, 2 );