Hi there @kel88. Thanks for joining in on this thread. The steps outlined above to change the date and time settings within your computer, as well as within QuickBooks will change the date format for your Invoices and Estimates as well. This leads me to believe that something may not be working as it should be and reaching out to our QuickBooks Desktop support team will be the best way to get to the bottom of this. Our highly trained support experts can do a screen share with you to help identify why the date format isn't changing after you make the appropriate adjustments, and can point you in the direction of some troubleshooting you can try resolve the issue. Use this link to get in touch with us when it's convenient for you: Contact Us.
I wish you all the best and know you'll get this resolved in no time!
