There are three main types of market entities, or "economic operators," that engage in the production, distribution, and sale of products. The lines of each and definitions may differ from your understanding, but these were set up to at least have decent definitions for this regulation.
All vintage/second-hand items that haven't been listed for sale to the EU prior to Dec. 13th, 2024 are be subject to the GPSR unless they are antique, art (designed to be art pieces, so nothing that "doubles" as art), and collectibles (rare and with historical and/or scientific value).