While you are of course correct on this, the amount of waste and environmental damage Russia is causing by blowing up dams and pretty much leaving a trail of garbage where ever they go combined with the pollution and wasted resources on burning fuel (both in engines and otherwise), destroying buildings and everything else going on, the couple truckloads of small LiFePo batteries on drones aren't even a rounding error in the equation.
I'm not an expert on what residual materials come from burning batteries, but I'm willing to bet that plastic from pretty much everything on the field has a bigger environmental affect, even the drones themselves are mostly just a plastic shell with very little of anything else in them.
It's and SMD led on a main board of the drone (at least on DJI ones) and the whole board is quite a complex computer with a ton of RF tech, power limitations and whatever is included to make those things both safe and fun for your average consumer. For a skilled operator it's not a problem to pull out the led and wire it to a transistor, but you need to pull the whole drone apart, somewhat sophisticated tools to solder wires to the led contact points, reassemble the whole thing excactly as it were and then connect that to the external harness.
Or, you can just bend the frame out of chicken wire, twist wires together and secure them with a tape or hot glue, zip-tie that to a drone and you're good to go. I think in Ukraine they use a ton of 3d-printed stuff which makes it more reliable and even easier to assemble. That way you don't risk breaking the drone and you can prefab pretty much the whole thing and just send them out to the field where practically anyone can assemble it even on standing in a mud puddle and have successful results within minutes from pulling a new drone out of a box.