Try this: When you get that window, click Continue. Then, in the window that appears, click Cancel. Quit Numbers and relaunch. That pesky What's New window should be gone (this worked for me).

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365