Both me and another new player have not been able to construct the first cairn in the game. We have all of the resources nessecary, have unlocked it via progression; Our main quest is to build it. The quest states to open the build menu. There is no such menu; guidebook only shows crafting and codex
Deleted the character and made another one. Now B is bring up a new build menu and working. Keybindnig was not changed.
I'm also having this issue. Havnt played since release. Made new character and unable to build the first cairn. Pressing B brings up the guidebook but the only option is crafting and codex. Build is COMPLETELY GONE.
Cairn is unlocked in build menu among all other free options and some other buildings.
If it's any help, the Build menu is hotkey B.
If you need to, in case things got swapped, there's a hotkey area in the options, that you can look at to find what your bind would be.