According to the Azure Cosmos DB documentation12, the change feed is a persistent record of changes to a container in the order they occur. The change feed outputs the sorted list of documents that were changed in the order in which they were modified.
The Azure function that has a trigger on the change feed receives all the properties of the updated items2. The change feed does not include the original items or only the changed properties. The change feed also includes some system-defined properties such as _ts (the last modified timestamp) and _lsn (the logical sequence number)3.
Therefore, the correct answer is:

Setting ConflictResolutionMode to Custom and using the default settings for the policy will not ensure that conflicts are sent to the conflict feed. You need to define a custom stored procedure using the "conflictingItems" parameter to handle conflicts properly.

Reference:
https://docs.microsoft.com/en-us/azure/cosmos-db/sql/how-to-multi-master
https://docs.microsoft.com/en-us/azure/cosmos-db/optimize-cost-regions

Explanation