VPN provider asks to install RootCertificate. How is it safe?

I want to use VPN provider (ProtonVPN), and don’t want to use an app. They ask user to install their Root Ca. How safe is it? What type of info could they get from my laptop? If I have their certificate installed, does that means they can see and get all info from my browser, including passwords and https sites? And what about other non browser traffic? How safe is it? What are the risks?