Thank you for posting here in the Community. Let me share some clarification about estimates in QuickBooks Online.
Currently, the option to know if a customer opened or viewed an estimate is unavailable. Right now, this feature is only available for invoices.
I appreciate your input about being able to view the activity on this type of transaction. We always update the features in QuickBooks Online, and this preference might be available in the future.
As we assess this, I suggest you visit our QuickBooks Blog to stay updated with all the changes.