Array to string conversion error on Laravel 9

I`m using Spatie to easily manage roles in my application. I decided to use it also for custom validation(since it's also using middleware for it)

I would like to display users which doesnt have role activated

To achieve this: I'm getting all users

$users = User::get();

and all Users with activated role

$activatedUsers = User::role('activated')->get();

untill this moment, everything goes smooth, arrays got the same structure, displaying different count of users(as intended) but when I'm trying to compare them using array_diff

$notActivatedUsers = array_diff($users, $activatedUsers);

Error:
'Array to string conversion' 

excacly on line 27 which is array_diff. I dont have any idea why it outputs this error