Understand why Vultr instances cannot use a NAT Gateway and public IP simultaneously.
No. An instance uses a single outbound internet path at a time, either through a NAT Gateway or through its own Public IP, not both simultaneously.
When an instance is assigned a Public IP, outbound traffic is routed directly through that IP. If the instance does not have a Public IP, outbound traffic can be routed through a NAT Gateway instead. These paths are mutually exclusive at the instance networking level because routing and source address selection are deterministic.
To provision a NAT Gateway for a VPC, see the NAT Gateway product documentation.