Susceptibility to Covid will likely be an interesting topic for PhDs for years to come.

We might have a slightly higher prevalence of some random genetic feature in Czechia that makes our death rate higher.

Overall on the map of Europe, it seems that death rates varied wildly and not according to usual patterns. For example, you would expect higher death rate in less developed southern Italy than in Lombardy.

I suspect most differences will be explained by what counts as a COVID death.

A valid point but Sweden used a very inclusive criteria. The only ones more inclusive I know of are Belgium and Peru.