Hi @StijnAvdL
To my knowledge and looking at the docs I don’t believe the retrieval of individual properties from something like a content picker field is currently supported. I also found this answer from March that suggests the same https://forum.umbraco.com/t/how-do-i-refer-to-a-nested-content-picker-value-in-a-label-template-with-ufm
The best you can do for now without some sort custom code would be to just use the content name instead.
For example {umbContentName: personPicker}