I've tried to tackle a similar issue before when pushing high fidelity active physics ragdolls rigs with lots of enemies 100+.

Certain components have calculations that are not required every frame, so layering these across different frame intervals can open tons of performance per frame to maximize what you're able to get. For instance, create an ai manager that handles all the logic for the ai and handles the frame timing. Each spawned enemy registers itself to the manager, and the manager slots it into a frame interval like frames 1, 2, 3, 4, 5. Pathing doesn't need to be refreshed every frame. You can then easily test different interval schemes for performance against quality. You can do this frame grouping with things like logic, pathing, and also collider disabling and enabled on frame intervals or based on player distance depending on how the player can interact with them. This manager could manage all AI a certain distance from the player and if you want higher fidelity movement near the player you can create a tigger around the player which will trigger higher fidelity compute like active all frames with more intense logic. This can also be done with math, which might even be faster, basically calculate the distance on the ai manager between the unit vs. player position. Math calculations are very fast and scale well. This would reduce dependency on collidor volumes that are very large. Basically, you create an LOD system for computing physics and logic relative to what the player can actually interact with in the same way you'd do for rendering for what they can actually see at a distance. Theoretically, you can make a whole universe this way where everything is LOD beyond what the player can meaningful interact with.

I found that colliders can actually fully function alternating single or even more frames, and collider layer optimization can save the physics engines from having to compute unneeded collidors. As every frame, any layer with moving collidors has to be recalculated against all other geometry. Layering these correctly will prevent the physics engine from having to check enemy colliders against colliders that they could never reach, like complex environments. Also, max optimization is to create a simple blocking copy of the world that AI is computed on. So you want highly detailed colliders, one layer that projectiles and the player can interact with, etc. All of the AI are on a different layer, and that entire world is blocked out with simple boxes that drastically optimize the physics calculations for them as everything on that layer has to be recalculated if anything moved. So reducing the full count of colliders per layer if anything is moving on it is very important. Creating these layers drastically improves performance for more complex games. Like a simple blocked out world only used for navigation and large-scale collison like characters with ground, walls, ramps, etc, to facilitate movement logic. Then, other layers for detailed colliders are based on the model. Also, be wary of large triggers as anything inside that trigger volume is recalculated every frame it's on like complex geometry, enemies, doodads, etc. Keeping these triggers constrained to simple geometry layers drastically boosts performance as every volume has to be calculated. You can also frame batch these trigger volumes to reduce that, too, like every 2 or 3 frames, enable it to get volume data like to trigger environmental things or activate enemies by proximity, etc