Scott's answer is a good one - you should read "The Norm Chronicles." But I think the question has a problem. Micromorts are a time-agnostic measure of dying, and the problem is that most risks you take don't actually translate well into micromorts.
Smoking a cigarette, which reduces your life expectancy by around 30 seconds, translates into either zero micromorts, or one, depending on how you set up the question. Increasing your relative risk of dying from cancer in 30 years isn't really the same as playing Russian roulette with a 1-million-chamber gun. Similarly, a healthy 25 year old getting COVID has about a 70-micromort risk based on direct mortality from COVID. But that number ignores the risks of chronic fatigue, later complications, or reduced life expectancy (all of which we simply don't know enough to quantify well.)
The answer that health economists have to this question is the QALY, which has its own drawbacks. For example, QALYs can't uniformly measure the risks of Russian roulette, since the risk depends on the age and quality of life of the player.
What we're left with is that the actual question we want answered has a couple more dimensions than a single metric can capture - and as I have mentioned once or twice elsewhere, reductive. metrics. have various. problems.