Not sure what you mean here. In the “traditional” internet peer to peer model from the early days, it was always a client-server model. Just that everyone “ran their own server”. For example: You want to send me email? Great my smtp server is sitting at my desk and the mail spool lives on my local hard drive.

That’s in contrast to the centralized model where all the servers live in a set of giant concrete boxes aka data centers run by hyperscalers.