What is the current system version (OS) for Nexus 5G, please?
You mean the LG Nexus 5?
That phone is end of life as of now and has not had any updates in some time…
Released in Nov 2013.
So it is 5yrs old.
Latest version is 6.0 Marshmallow.
Per https://developers.google.com/android/ota, the latest available system software for the Nexus 5x is 8.1.0 (OPM7.181105.004, Nov 2018).