Hi sys718. Thank you for reaching out to the Community.
QuickBooks Desktop Mac 2021 (QBDT Mac 2021) has not been officially tested with macOS Tahoe (version 26), as QuickBooks has officially discontinued the product. While QBDT Mac 2021 may still work, you may encounter compatibility issues when running it with a newer macOS version.
QBDT Mac 2021 has specific system requirements. You can refer to this article to learn more: System requirements for QuickBooks Desktop for Mac 2021.
You may consider upgrading to a newer version of QuickBooks Desktop for Mac to ensure compatibility with the latest macOS.
Should you have any other questions, feel free to respond here.