Yes and No. For example, "type: LoadBalancer" works fine on almost every cloud, but various annotations need to be added for SSL termination on an AWS ALB, for example. The annotations don't collide tho, so you can have a load balancer with both AWS and Google Cloud annotations, and it will work fine on either cloud.
Volume classes are probably the best example of being cloud-specific, but this problem is solved by having a different volume class for each cloud provider, named the same, such that the deployment can always grab a disk regardless of which cloud its living in.
They are. Kubernetes has abstractions at exactly the right layers (e.g. Service to create a load balancer) so that you can exchange configs between cloud providers.
There can of course be some difference in the capabilities that each cloud provider supports (e.g. not all load balancer implementations may support UDP) but the abstraction is definitely there.
I thought load balancers popped out the end of Services and it was plugins that handled the specific cloud environment? I'd say that still constitutes cross platform.
Volume classes are probably the best example of being cloud-specific, but this problem is solved by having a different volume class for each cloud provider, named the same, such that the deployment can always grab a disk regardless of which cloud its living in.