Explanation
To track clicks on Contact records in Salesforce, two requirements must be met:
The subscriber key must match the ContactID field in Salesforce.
The individual level tracking option mustbe selected in Marketing Cloud configuration.
If either of these requirements is not met, clicks will not show up on Contact records. References:
https://help.salesforce.com/s/articleView?id=sf.mc_co_marketing_cloud_connect_configuration.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.mc_co_subscriber_key_guidelines_for_marketing_cloud_connec