You should create an Integration subnet. Virtual Network integration requires a dedicated subnet in your Virtual Network. The subnet should have a minimum of /28 blocks to accommodate the App Service instances.
You should also use the Premium App service plan. Virtual Network integration requires Standard, Premium, Premium v2, or Premium v3 App service plans.
You should not create a Network Security Group. With Virtual Network integration, you can control the outbound traffic from your App Service using NSG rules. Inbound rules do not apply to the App Service. This also means that even if you enable Virtual Network integration, the App Service does not become private to your Virtual Network. This scenario does not suggest blocking any outbound traffic.
You should not use the Isolated App service plan. This plan is used for App Service Environment and is already deployed inside a Virtual Network.
You should not create Azure Virtual Network gateway. The App Service and Virtual Network are in the same region. Regional VNet integration does not require a Virtual Network Gateway. If the Virtual Network is in a different region or is deployed using a classic model, then a gateway is required to establish connectivity.
https://learn.microsoft.com/en-us/azure/app-service/overview-vnet-integration
https://learn.microsoft.com/en-us/azure/app-service/configure-vnet-integration-enable