2 days ago - Shurenai - Direct link
The big single wooden spikes are indeed gone for several reasons- Most notably that they were exploitable due to how they functioned. They probably aren't coming back any time soon.. but there's mods that re-add them.

Catwalks however still exist; Just not in the form you remember.

Instead of having a hundred different blocks that you have to craft, you now just craft material frames, which you can then use the Shape Menu to pick from 1300~+ shapes to build with- Catwalks are in this shape menu, iirc.

To access the shape menu, hold a material frame in your hand, and hold R to bring up the radial menu- Select the icon that has 3 basic shapes. Tapping R should also bring up the shape menu directly. (If you've remapped your reload key, whatever your reload key is should work)

Keep an eye out for that shape menu icon on things in your inventory; Whenever you see it, the item has shape menu options. For example, your bedroll has multiple colors you can pick between.

Similarly, Most furniture has been condensed from dozens of different options into several; Storage objects, Wooden Furniture, Metal Furniture, Cabinets, etc; Each of which has a shape menu.

Edit: Overall, I would say there's been a massive upgrade to building- We now have access to nearly every shape in the game, where we used to be far, FAR more limited in our building choices.