Marketo Activity object API's missing High Watermark / Audit Fields. Also Is there any Object in Marketo for Object and Field Metadata, which can be retrieved dynamically

Marketo Activity object API's missing High Watermark / Audit Fields. What is the potential way to identify changed records using UpdatedAt or ModifedDate like columns. None of the Activity Objects having this Audit column. What is best possible way to identify delta considering API limits

 

Also Is there any specific Object in Marketo for Field Metadata, which can be retrieved dynamically based on each Object filter to make the orchestration Dynamic. Basically looking for a system table in marketo which can be used as a data source and each Marketo object can be passed from Grid Variable to store the Field names in to a separate grid variable to use later

 

Did anyone face this kind of scenario before? Please share your experiences