You can put links to any completed work in your portfolio, as long as the client is OK with you doing so. However, entries pertaining to completed Upwork contracts are usually considered more "valid", as they're easily verified to be your own work.
Kyveli M wrote:
Hello, I would like to make a question about the portfolio. This field refers only to jobs completed through the platform of Upwork or to any previous work?
Thanks in advance.
On top of Michael's advice, you can also include work samples that were not sold to any client, such as work that you have done during your studies or in your free time, as long as you own them and don't disclose any classified data.
Seeing your field, you probably don't build a lot of houses as a hobby, but still