My country of Belgium. Unless by "100 % renewable" you include fossile gas generation "offset" by summer's overproduction (which would be disingenuous).

Middle of January: 100% overcast for weeks on end with only 8 hours of daylight, some days with little to no wind. Geography does not support more hydro or any geothermal generation. Country is way too densely populated for meaningful biomass fuel production (not that it is a climate-friendly practice anyway).

Maaaybe there is a stretch argument to be made about offshore wind/water, but we have relatively little coastline and very busy waterways due to having some of the busiest shipping ports of Europe, so I doubt even in the most optimistic scenarios this can fill the gap during the winter season.

For any meaningful definition of the concept, we can't be 100 % dependent on nationally-sourced renewables until we figure out much much denser and cheaper long term storage solutions. Which is alright - maintaining existing nuclear reactors is an option (barely due to legaislative sabotage pushed by the "greens" but a couple gigawatts is nothing to scoff at) and more importantly we are part of the EU which will hopefully allow us to buy southern European solar/wind via HVDC lines in the future, and we're already very dependent on French nuclear. (Also we don't have to be 100 % independent to push for renewables, perfect mustn't be the enemy of good and all that)

Vatican City /s

I think that there are constraints for certain countries, but the majority probably could. And when they can't, it should be solved by cooperation and trade, IMHO.