Considering the controller recommendation in the intro I guess the mouse+keyboard control method and in particular the remapping/rebinding functionality was not tested that thoroughly?

Interact/Use for example seems to be hardcoded to 'E' and can in fact not be reassigned another key. Or it can, but certainly not via the remapping menu, since Interact/Use is nowhere to be found.

The labeling could be clearer in some places as well, I've yet to figure out the purpose of 'CursorHorizontal' and 'CursorVertical' or why there's 'Quick Turn +' and 'Quick Turn -'.
'fix for Quick select range icon bug' towards the bottom of the list is likely a debugging remnant and could be removed altogether too(?).

There's also this floating tree next to the spot where you first use the C.O.T.A.C. radio.

It's also impossible to reassign the same keys for multiple actions.

While default WASD is simultaneously working in different contexts like character movement, moving in the inventory, moving the focus in the UI in general, it doesn't for any other keys like TFGH or IJKL because they're not accepted to be assigned in more than one instance.

Same for the arrow keys. Default actions for the left and right arrow key are both for rotating the map and horizontal camera nudge, but as soon as you try to reassign to something else for these two contexts it's denied and you're forced to use entirely different keys for either action.

Not an ideal solution but until the remapping issues get hopefully fixed with a future patch or update you can work around the deficiency with AutoHotkey.