It's no longer a single dedicated menu. The commands that were available under designation are available on the bottom bar.

Digging: "Setting digging orders (m)" will open a sub-menu containing regular digging, stairwells, channels, ramps, and Remove Construction

Chopping trees: Available directly on the menu; hotkey is l.

Plant gathering: Available directly, g

Smoothing and engraving (v): Submenu includes smoothing, engraving, mine carts, and fortifications.

The last button is to remove designations (x).

All of these buttons, except remove designation, have advanced options for setting the priority.

Traffic settings are on the far-right of the buttons, hotkey is T

It's no longer a single dedicated menu. The commands that were available under designation are available on the bottom bar:

• Digging: "Setting digging orders (m)" will open a sub-menu containing regular digging, stairwells, channels, ramps, and Remove Construction
• Chopping trees: Available directly on the menu; hotkey is l.
• Plant gathering: Available directly, g
• Smoothing and engraving (v): Submenu includes smoothing, engraving, mine carts, and fortifications.
• The last button is to remove designations (x).
• Traffic settings are on the far-right of the buttons, hotkey is T

All of these buttons, except remove designation, have advanced options for setting the priority.