Unable to add a default route to the routing table: Rules in the route table must use private IP

Summary:

I'm unable to add a default route, getting an error "Rules in the route table must use private IP as a target. Or the route table can be empty (no rules)."

Content (required):

I'm trying to create a VCN manually. I created the VCN, subnet, default gateway, routing table.

But not able to add the default route and the instance isn't reachable without it.

I select Target Type: Internet Gateway, Destination CIDR Block: 0.0.0.0/0, I select my Internet Gateway, and it won't let me add it.