How-To sell used items safely and privately (example is "Xbox Series S")

Scott

In Switzerland, all online portals for used items are owned by a large corporation (https://swissmarketplace.group/). You have to verify your phone number, i.e. you can't sell anonymously.

How can I sell used tech items as anonymously as possible in Switzerland? Here, for example, Xbox Series S.

I understand of course that they don't want stolen items to be sold, but I still don't want to reveal all my personal data.

Thank you