Dota Underlords was an experiment by Valve on their Steam Early Access platform, and was the first mobile game published by the company using the Source 2 engine. The game was an auto battler available on both PC and mobile devices.
It seems though that the experiment has failed, as player popularity based on peak concurrent users has dropped over 90% since launch.
The game had nearly 200,000 concurrent players according to Steam Charts when it launched, but in recent weeks has been peaking at just 15,000.
The more worrying fact is that this shows no signs of slowing, as popularity is on a consistent downslope, even with new updates being released. While the game has mostly positive reviews on Steam, it seems that players aren't sticking with the game.