Many protocols use an ephemeral private key, and protocols like TLS that don't today are moving toward ephemeral private keys faster than they are toward PQC.

Many protocols use an ephemeral private key, and protocols like TLS that don't today are moving toward ephemeral private keys faster than they are toward PQC. The ephemeral key gets signed with your long-lived private key, but that's all your long-lived key is used for.