I wrote shell and python scripts as a wrapper for ngctl dot (netgraph Graphviz export) and dot (Graphviz dot to png). Available through my repository :
a. Coideberg: https://codeberg.org/maulanahirzan/Netgraph-Viewer
b. Brew : https://brew.bsd.cafe/maulanahirzan/Netgraph-Viewer
These scripts requires root to run so: choose sh version for less external dependencies (more secure), or python version bundled with tkinter image viewer.
!!! Run these script with extra precaution. I am not responsible for any broken system or data lost. You have been warned !!!