In general this is true. But routers/loadbalancers exist for many TCP protocols (even stateful ones) as well. gRPC is probably the most popular such protocol at present.
I think you mean application protocols. There's only one TCP protocol. In the example of gRPC you'd have gRPC > http/2 > TCP > IP > ethernet
Yes load balancers can make decisions on application layer protocols like gRPC, but not in mode TCP which is what the parent comment was asking about. That's because that mode only looks at the TCP header and IP headers which don't contain any information about the application protocols.
An example of a time you might use this mode is if you're terminating TLS on the web servers, so you can't read the encrypted http headers when they hit the load balancer.
