Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
Your observation is correct.
- Internet routing preference is only compatible with zone-redundant standard SKU of public IP address.
- Basic SKU of public IP address isn't supported
There is no way to configure the Basic IP to use Internet Routing preference.
However, please note that both Microsoft Routing and Public Internet (ISP network) Routing come under Internet Egress only
- See : Azure Bandwidth Pricing
- Inter Region refers to data transfer between regions within Azure like Global Vnet peering or Vnet to Vnet traffic
This means,
- Changing the Internet egress traffic routing will have no impact on the Inter-region traffic charges
- If you have a Global Vnet peering or Vnet to Vnet traffic, it will always be charged under the Inter-region bandwidth pricing.
Thanks,
Kapil.