These countries do not exist. There is no county getting by without burning fossil fuels or using nuclear for baseload somewhere. The 100% you might be thinking of are countries that import fossil/nuclear baseload during lulls and export spare renewables during high generation times for a “net 100% renewable”. This is a start, but it’s marketing bullshit because it’s not actually sustainable for all countries to do that. Someone needs to provide baseload.

Which countries? The closest I know of is Norway. But they do burn some gas and also import from Sweden (and others). Even if they didn't have gas I don't think it is fair to say that a country runs on 100% renewables if they import energy from a country that isn't 100% renewable.