Good day, layniberlin.
Have you tried downloading or previewing the estimate after creating it? If not yet, I suggest you do so to see if the error occurs on your end before you sent it or on your client only.
Find and open the estimate. Make sure that there is information in the Description field, then click the Print or Preview button. If it looks good, then then the issue is on the client's end only. If not, we need to perform some troubleshooting steps.
All we need is to update, repair, or re-install Adobe Reader/Acrobat. This is what QuickBooks Online uses when viewing sales forms and other documents. You also want to advise your customer to do the same.
Here's the link for more details about estimate: Set up and send progress invoices in QuickBooks Online.
Post again if you have more questions. Stay safe and healthy!