I've got some troubleshooting steps to help you with your missing or greyed-out tickbox to clear/reconcile a transaction in QuickBooks Online (QBO), GrayHair. I'll walk you through the process below.

The reason the tick mark box for manually reconciling/clearing a transaction in QBO is missing could be that the option to show the Reconcile and Banking Status in the Account History settings could be turned off. Here's how to fix it:

1. Go to the Transaction tab.
2. Select the Chart of accounts.
   
3. Locate and select the account your transaction is associated with, then click the Account History.
   
   
4. In the Account History menu, click the Gear Icon (Settings).
5. Make sure to tick the Reconcile and Banking Status checkbox.
   
   
   

However, if the tick mark box is greyed out and you've already tried using different browsers, I recommend using your QBO in a private browser. This way, you can rule out any issues related to cached data or cookies that could affect the functionality. You can use these shortcut keys to access a private browser:

• Safari 11 or newer: ⌘+Shift+N
• Chrome: Ctrl+Shift+N
• Firefox: Ctrl+Shift+P
• Safari: Command+Shift+N

Once you're in a private browser and can reconcile or clear a transaction, proceed to clear the browser's cache. Refer to this article for more details about how to clean a web browser's accumulated data: Clear cache and cookies to fix issues when using QuickBooks Online.

In addition, you can visit this article to learn about printing or exporting your reconciliation report to Excel, which facilitates easier data retrieval: View, print, or export a reconciliation report in QuickBooks Online.

We're still available to assist if you have any further questions about reconciling bank transactions in QuickBooks Online (QBO). We'll be happy to help. Have a great day!