Since it's highly unlikely that the lethality of the virus depends on which continent it's on, a more likely explanation is that people in the US are more likely to belong to any of the risk groups by being obese or by having diabetes.
The total number of covid-19 dead that were younger than 45 in the countries that EuroMOMO covers is in the low thousands, while the total number of covid-19 dead is in the low hundreds of thousands. That's two magnitudes lower risk compared to the general lethality.
Every individual has to do their own risk analysis, and see if they belong to any of the risk groups for covid-19, because that changes the individual equation.
That doesn't affect mortality, except that the more a country gets infected the better mortality will look since susceptibility to infection just happens to correlate to susceptibility to severely bad outcome
Check the number of deaths by age group at EuroMOMO: https://euromomo.eu/graphs-and-maps
The total number of covid-19 dead that were younger than 45 in the countries that EuroMOMO covers is in the low thousands, while the total number of covid-19 dead is in the low hundreds of thousands. That's two magnitudes lower risk compared to the general lethality.
Every individual has to do their own risk analysis, and see if they belong to any of the risk groups for covid-19, because that changes the individual equation.