I wonder how much of their own guidelines they violated with MacOS Tahoe.

As they should. There are fundamental differences in hardware and capability between 1992 and 2026.

The most immediate are pull-down menus at the top of the screen. They work good on a 9 inch screen, they are awful with 27 inch displays.

Another related change are modal dialog boxes. When you have a 9 inch screen you're fundamentally looking at one document in one app at a time. When you got 2 27's that's not true anymore.