Hi @NGroupApS,
If you want this to happen automatically, this would require a Professional subscription with access to workflows. Under Menu > Automation > Workflows, you would set up a contact- or deal-based workflow which could look like this:
If you’re using the free CRM or a Starter version you don’t have access to workflows. In this case, I would recommend setting up a filtered contact view. First, under Menu > Contacts > Lists, create a list that filters for contacts with “Last activity date is more than 4 days ago”. Then, navigate to Menu > Contacts > Contacts and click All filters to filter for List membership in the list created a moment ago. Via Actions, you can add the Last activity date as a column and sort the filtered view by it. Then, click Save view > Save as new and name it accordingly. This would now dynamically update with inactive contacts.
For deals, you can customize the board view to show this automatically. Under Menu > Sales > Deals, click Board actions > Edit cards > Mark cards inactive after 4 days.
Hope this helps!