Show old members their last level and hide other levels from active members on levels page.

my_pmpro_hide_levels_for_active_and_old_members.php

<?php
/**
 * Show old members their last level and hide other levels from active members on levels page.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_hide_levels_for_active_and_old_members( $levels ) {
	// Bail if no levels.
	if ( empty( $levels ) ) {
		return $levels;
	}

	// Bail if the user is not logged in.
	if ( ! is_user_logged_in() ) {
		return $levels;
	}

	$user_id = get_current_user_id();

	// Get user's current levels.
	$user_levels = pmpro_getMembershipLevelsForUser( $user_id );

	// If the user has levels, show these levels only.
	if ( ! empty( $user_levels ) ) {
		return $user_levels;
	}

	// No active levels, get the user's last level.
	global $wpdb;
	$user_last_level_id = $wpdb->get_var(
		$wpdb->prepare(
			"SELECT membership_id FROM {$wpdb->pmpro_memberships_users} WHERE user_id = %d ORDER BY id DESC LIMIT 1",
			$user_id
		)
	);

	// If they had a level in the past, show that level only, else show all levels.
	if ( ! empty( $user_last_level_id ) ) {
		$user_last_level_id = intval( $user_last_level_id );
		foreach ( $levels as $level_id => $level ) {
			if ( $user_last_level_id !== $level_id ) {
				unset( $levels[ $level_id ] );
			}
		}
	}

	return $levels;
}
add_filter( 'pmpro_levels_array', 'my_pmpro_hide_levels_for_active_and_old_members' );