Realm List Error (Swift): Generic type 'List' specialized with too few type parameters (got 1, but expected 2)

Question

I'm following the MongoDB Realm documentation and in one example I get the following error:

How can I fix this?

Context:
Realm: 10.26.0
RealmDatabase: 11.17.0

Realm documentation: https://www.mongodb.com/docs/realm/sdk/swift/examples/define-a-realm-object-model/#std-label-ios-define-a-to-one-relationship-property

Many thanks in advance!