Visibility and Targeting without Raycasting?

Hi guys, I am making simple AI, for my 3D shooter, using OpenGL and C++

I was using raycasts at chest height, in an arc to detect enemies, as that was my strategy for this in 2D.

This is not very good, depending on distance, and elevation, and if I want to add a cone of rays, that will destroy performance even more, as I want to be adding a lot of bots to be constantly shooting at the nearest threat, and constantly reassessing threats.

In my last 2D game, I used multiple layers on the map each A*'ing asynchronously to stuff that needed to be avoided or attracting, but all the enemies were slow and melee in that, so it kind of worked, and also the POIs were stationary, so it made sense.

What are the currently state of the art solutions for doing LOS checks at scale, or doing "search cones" without physically raycasting cones for every unit or giving divine knowledge ?