ProtonVPN, like other VPN services, requires a username and password for authentication. Here are some general points to consider:
On mobile (Android), you can "Continue as guest" to use free features without an account, though an account is mandatory for premium features. Key Features Review How to use Proton VPN on Android protonvpn username and password
Using a VPN is about privacy, so protecting the keys to that privacy is essential. How to manually configure OpenVPN for Proton VPN on Linux ProtonVPN, like other VPN services, requires a username