Here is my own Build.
I got some luck to found someone selling this riven, I use only one gold elemental mod mostly for the status chance.

Mine has a fire base, with the base weapon's elemental damage you get around 800 elemental damage instead of 400. (for combined elements, mine is radiation with fire element as weapon's base elemental damage, just change [High Voltage] for whatever you want).

With secondary fire mode (while aiming), you can deal around 50K damage per shot in the head.

Add, if you can, Primary Mercyless (more usefull on full auto mode) or Deadhead (for Burst mode) if you want get bigger damage, you can get up to 100k damage on headshots.

For more informations about Kuva Liches and the Kuva weapons, go check the wiki: https://warframe.fandom.com/wiki/Kuva_Lich.