@Anders Madsen Welcome to QnA platform and thanks for your query.
I tested setting unifiedssp page contract 2.1.0 in my tenant and found that certain built-in strings such as "Email Address" string on sign-in page is not getting translated. This works with page contract 1.2.0 and 2.0.0 as well.
I will report this issue to the B2C product group. You may also open a support ticket and get a bug raised regarding this issue, so that you can check for the updates as well. Meanwhile this is not fixed, you can use page contract version 2.0.0 for unifiedssp.
-----------------------------------------------------------------------------------------------------------
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.