@lignuss this is a typical job for http Middleware, see: https://laravel.com/docs/9.x/middleware. You can assign middleware to a single route or a group of routes, the documentation explains all of this.
You can create a middleware that checks if the user is an admin or not, if it is not an admin you can redirect them to the client page or show an error message.
If you are not that experienced with middleware, this google search should give you some good answers: https://www.google.com/search?q=laravel+middleware+admin+only