Every body is different, but generally for most people every 2-3 days tends to be the sweet spot for a full shower with shampoo, conditioner, etc.

Personally, I have greasy hair problems, and I ultimately found that showering less frequently made the biggest improvement of all of the changes I made. I'll generally shower every 2-3 days, and if I do something that makes me sweaty I'll hop in the shower and rinse off without using any product between those every other day showers

On the other hand, for OOP, they're making some big changes and probably need the consistency of every day to help maintain the habit they're building