Linux has no such features as pledge or unveil, nor capsicum. it has cgroups, namespaces and a mess ofnother things u need to combine to try and do similar things. (it was built iteratively as many systems interacting and being combined to form 'sandboxing' or isolation/limiting of capabilities rather than specific isolation as an entire concept with specific system calls and kernel paths to enable it).

there might be newer stuff in linux land now i see comments about landlock but i assume those will build on the linux primitives rather than whole new ones. - total assumption there but it would seem logical to reuse rather than make new.

part of likely what they mean by 'mess' is that its all over the place. many different ways to try and lock things down. hard to pick what is best etc. without thoroughly diving into the different subsystems entirely. (as opposed to just have 1 or 2 relatively simple system calls)