[2024] Die one time?

Steam is just being derpy. You earned the 'Die 1 time' achievement a long time ago, and the achievements were recently redone from top to bottom. When they did so many players retroactively got achievements that were broken, re-recieved achievements they already had due to steam tracking your progress in order to give achievements in the first place, etc.

I don't know why steam took so long to inform you you got the achievement though. But, it's like, 99.9% chance that it's nothing to worry about.