Add a "Requires Membership" column to the Categories dashboard page to show what levels are required to view.

requires_membership_categories_columns.php

<?php

//add a new column to the categories view
function requires_membership_categories_columns_head( $defaults ) {
    $defaults['requires_membership'] = 'Requires Membership';
    return $defaults;
}
//get the column data
function requires_membership_categories_columns_content( $content, $column_name, $term_id ) {
	if ($column_name == 'requires_membership') {
	    global $membership_levels, $wpdb;
		$protected_levels = array();
		foreach($membership_levels as $level)
		{
				$protectedcategories = $wpdb->get_col("SELECT category_id FROM $wpdb->pmpro_memberships_categories WHERE membership_id = $level->id");
				if( in_array( $term_id, $protectedcategories ) ) {
				$protected_levels[] = $level->name;
			}
		}
		echo implode( ', ', $protected_levels);
	}
}
add_filter( 'manage_edit-category_columns', 'requires_membership_categories_columns_head' );
add_action( 'manage_category_custom_column', 'requires_membership_categories_columns_content', 10, 3 );

This recipe is included in the blog post on "Show a Post, Page or Category’s Required Membership Levels in the Dashboard “All” Views" at Paid Memberships Pro here: https://www.paidmembershipspro.com/show-post-page-categorys-required-membership-levels-dashboard-views/