Add capability to a specific user - Add 'manage_options' capability to an non-admin user. https://www.damiencarbery.com/2020/06/add-capability-to-a-specific-user/

add-manage-options-to-user.php

<?php
/*
Plugin Name: Add capability to a specific user
Plugin URI: https://www.damiencarbery.com/2020/06/add-capability-to-a-specific-user/
Description: Add 'manage_options' capability to an non-admin user.
Author: Damien Carbery
Author URI: https://www.damiencarbery.com
Version: 0.1
*/


function dcwd_cap_filter( $allcaps, $cap, $args ) {
	//error_log( 'AllCaps: ' . var_export( $allcaps, true ) );
	//error_log( 'Capability: ' . var_export( $cap, true ) );
	//error_log( 'Args: ' . var_export( $args, true ) );
	$user_to_escalate = 4;  // ID of the user to add the capability to.

	$capability_to_check = 'manage_options';  // Can change to 'activate_plugins' etc.

	if ( $capability_to_check == $cap[ 0 ] ) {
		if ( is_user_logged_in() ) {
			$user = wp_get_current_user();
			
			if ( $user_to_escalate == $user->ID ) {
				$allcaps[ $capability_to_check ] = true;
			}
		}
	}
    return $allcaps;
}
add_filter( 'user_has_cap', 'dcwd_cap_filter', 10, 3 );


// Don't use this "permanent change" version.
/*function dcwd_add_manage_options_capability() {
	$user_to_escalate = 4;
	
	if ( is_user_logged_in() ) {
		$user = wp_get_current_user();
		if ( $user_to_escalate == $user->ID ) {
			$user->add_cap( 'manage_options');
		}
		return;
	}
}
//add_action( 'admin_init', 'dcwd_add_manage_options_capability' );
add_action( 'init', 'dcwd_add_manage_options_capability' );
*/