Instructing sales reps to follow their opportunities and using Flow with a scheduled action and an email alert are two solutions that can meet the requirement of sending a notification to sales reps when their opportunities remain open past the close date. Following an opportunity allows sales reps to receive updates and reminders about the opportunity in their Chatter feed. Flow with a scheduled action and an email alert allows you to automate the process of sending an email notification to sales reps based on a time-based condition, such as the close date. Verified Reference:
https://developer.salesforce.com/resources2/certification-site/files/SGCertifiedSalesCloudConsultant.pdf (page 21)
https://help.salesforce.com/s/articleView?id=sf.collab_feed_follow_records.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.flow_concepts_scheduled_start.htm&type=5