You have downloaded the package and trying to install the individual package. You need to add the testing repo and install the package from there (using apt-get) so the deps are also installed.
Try the procedure shared here...
Yes - https://archive.raspbian.org/raspbian/pool/main/n/nnn/
It's on Raspbian Testing.
Also, I mentioned _runs on_ which doesn't necessarily mean it's available in the default repos.
This post is a shameless attempt to introduce nnn - https://github.com/jarun/nnn
I've been writing `nnn` for a year and it's stable now. Available on several distros and each release comes with cooked packages for multiple distros.
`nnn` runs on Linux, OS X, Raspberry Pi, Cygwin, Linux...