Hello @Frank Nguyen , Thank you for reaching out. As mentioned above by Alan, the current limit is 1 VPN gateway per Vnet. However, just to add additional details you can create multiple connections to the same VPN gateway. When you create multiple connections to the same VPN gateway, all VPN tunnels share the available gateway bandwidth. You can refer top this document to explore VPN gateway SKU's and their limitations.
You can also go through this documentation for additional Networking limits.
Please let me know if there are any additional concerns.