When you enable Always-on VPN on a Personally-Owned Work Profile policy, Android enforces a device-level security requirement as a prerequisite. Specifically: Android requires a screen lock/password to be set on the device before Always-on VPN can be activated. This is an Android OS-level enforcement, not Intune imposing it directly.

The default Password Complexity is None

Setting this to Low allows the user to continue with 6 Digit Passcode for device