Picom
From NixOS Wiki
picom is a standalone compositor for Xorg, suitable for use with window managers that do not provide compositing. picom is a fork of compton, which is a fork of xcompmgr-dana, which in turn is a fork of xcompmgr.
Installation
Put the following line into your system or home-manager config to install picom and enable it's service:
services.picom.enable = true;
If you just want to install picom without automatically running it every time your system boots, use this instead:
packages.picom.enable = true;