I don’t think there is much more than what was shared already.
Except for maybe the obvious:
Adapt or change the landscape so as to have less visible foliage. Canyons/high buildings/view blockers of any type including rocks/mountains.
Also,
Dead/leafless trees cost less - use more dead trees.
Since unreal is incapable of handling lush landscapes with decent performance, don’t have lush landscapes… as silly as it may seem.
After the basic changes:
You want to test/bench your worse case scenario (max #of landscapes - 4, max foliage, max overdraw, max tris count etc).
On your lowest spec supported device:
For this, you need to make sure your scalability is at the lowest, and that your materials perhaps even instance count (on things like grass) also take scalability into consideration.
Once that runs OKish, then you need to Benchmark your worse possible scenario, at the highest res you really want to support (hint, with unreal its not 4k), on the device with the max specs you want to support.
Based on that benchmark, you will then take the instance count down to where the rendering MS cost of the full base scene is around 10frames per second below acceptable.
The extra frame time will come in handy later, when you add stuff that you didn’t think of needing or introduce some gamplay gimmic of some sort that eats up FPS.
Ideally, this will only benefit the lower performing setup you already got to run somewhat decently. But you probably want to check and make sure rather than accept it on faith.
That’s really all the stuff there is to mention about it - save for some newer engine trash or settings I’m not prevy to.
Also worth noting that this testing/bench process would never change regardless of what engine you decide to use…