Bonus question: How many names would one need to right down?
Real bad luck some chud hog like Light Yagami found the Death Note before anyone else did. By killing only criminals reported on in the news, he effectively made himself into a weapon of execution that could be freely wielded by the cops at almost entirely their own discretion. I wish the anime would have explored that idea a bit more, but I'll settle for the very pathetic way Light Yagami got caught by a 12 year old, threw a tantrum, and then died. That was unironically a great ending.
So say a communist found it instead. How much damage could this baby do to the global capitalist nightmare we live under?
About 60 million people die each year. You'll give yourself carpal tunnel before you cause enough of a mess for epidemiologists to get suspicious.
It's hard to kill a large number of people who don't already have mainstream news articles or local news articles or wikipedia articles with a Death Note unless you're ordering used high school year books off ebay or using facebook to find local targets in your area.
The QAnon types make conspiracies when nothing happens, the epidemiologists will notice the an increase in notable deaths when the news and data confirm the presumed non-sense by the tin foil hat types.
When two or three celebrities die in the same year/month, people get out the conspiracy theories. They will notice.
Covid gives you perfect cover. "Died suddenly of blood clots". Hell, the GOP's collective refusal to mitigate Covid in any way even makes them like 4x more likely to die compared to Libs, so you can pretty much go hog wild there.