Hi Signe,
As you know, Upwork is not involved with the formation or negotiation of service contracts between parties on the platform. Nor can Upwork provide legal advice or advise you as to how the Terms of Service applies to or affects third-party rights.
However, if you and another user agree to use the
Optional Service Contract Terms for your engagement, section 6 contains
terms related to ownership of intellectual property. Please note that
you and another user you contract with may negotiate additional or different terms than the default terms contained in the Optional Service Contract Terms. We encourage you to consult with an advisor or legal professional if you require additional clarity.
~ Valeria