Where I live it's 90 degrees or higher, and humid in the summer, and can be sub-zero in the winter. It's also quite hilly -- flat and level riding is the exception. I'm not riding a bike any substantial distance in those conditions, regardless of paths or lanes.
For heat specifically, you need trees covering sidewalks and bike paths. Also the materials you build sidewalks and structures with contribute to this, and if you can then adding some evaporative cooling via fountains or ponds is a great idea too. For more ideas: https://www.epa.gov/heatislands/heat-island-cooling-strategi...
The heat island effect is real, and it's only going to get much much worse in cities that refuse to work to fix it.
Bike lanes are plowed and/or compacted multiple times a day during heavy snowfall. Albeit it isn't really that hilly but more than weather, the main constraint is having a city willing to actually maintain biking infrastructure.
I found that on an electric scooter with a full helmet I was totally warm at high speed into icy wind coming off the sea. Warmer than say just standing outside for a few minutes with a hat and scarf but my face not covered.
On those days it’s a little less fun than the other 95% of days, but still feasible. And even I didn’t brave those extremes, 95% of days biking is a lot more than 0%.