Would be helpful to see a split between widowers and young adults.

Doesn't explicitly say widowers but still relevant:

"Older people are most likely to live alone: 34% of those over 65 do so, and among those aged 85 and older, the share jumps to 56%. But young adults between 25 and 34 also stand out, with 28% living alone — well above average. Women live alone slightly more often than men (21.2% versus 20%)."

https://www.dw.com/en/germany-sees-uptick-in-people-living-a...

That explains change over time, but for me the strangest part is the discrepancy between countries. I would've expected the US to be the highest