I'm too new in this area of computing to be able to tell what your understanding
is of either of those terms.

Nim can do memory management with any backend depending on what you mean by
it.
You can allocate and deallocate memory regions with pointers and manage those
yourself entirely manually (I do this sometimes with the C backend).
You can manually call the automatic hooks that nim inserts to manipulate
ref-counters and deallocate memory when that counter reaches 0. You can also use
hooks more generally to manage how that memory is treated
(https://nim-lang.org/docs/destructors.html#about-this-document).