Zelensky says about 30,000 to 35,000 Russian Soldiers are now killed every month in Ukraine and Russia primarily with Drones

Though I'm not there I can I think understand how this would be or could be done. It would likely mostly be done at night but also in the daylight too. At night there are less people awake and likely less people tracking things like this as well especially if they are traveling at 10 to 100 feet in altitude as they move which is below radars basically. Because Radar covers the contours of the earth. But, it's likely all kinds of different drones would be used in these deaths. It's unfortunate that Russia doesn't protect their soldiers very much from "Death by Drones". 

So, these drones could be the 300 dollar versions or the 35,000 dollar versions which are more like the Iranian Shahed drones reverse engineered by Ukraine and the U.S. and other NATO countries now and Ukraine is sharing this technology with the non-Iranian Arab countries throughout the middle East at this point too in order to better protect themselves from Iran and Russia who are now fighting against the U.S. and Israel together with many drones and missiles (even though Russia isn't setting off the missiles they and drones in the middle east they are building them and sending them to Iran to set off on oil processing facilities or oil wells or in the straight of Hormuz on ships or U.S. military bases as well.

So, anyway, the best time to take out Russian soldiers likely would be at night when less people could hear or see these drones of one kind or another. So, it could be the 300 dollar type of small drone that carries a hand grenade that would be dropped into a group of soldiers outside or a larger drone with some kind of bomb that blows up where the soldiers are eating or sleeping inside some kind of bunker. This is what appears to be going on when 30,000 to 35,000 Russian Soldiers are dying from Ukraine Drones now every month in Ukraine and Russia.