Forage: Offers "Virtual Experience Programs" that take 5–6 hours to complete. They are free, open-access, and you can put the certificate on his LinkedIn.
Extern: Specifically focuses on 8–12 week remote projects for Fortune 1000 brands. It's great for gaining "real" experience if he feels his resume is currently a bit light.
Wellfound (formerly AngelList): The go-to spot for startup jobs. You can filter specifically for "Remote" and "Internship" roles in tech, marketing, or operations.
Y Combinator (Work at a Startup): Features roles at some of the world’s most innovative new companies. Many offer remote summer or semester-long internships