I biked year round for 4 years in Washington DC. Biking by 40ºC and in the snow in the winter wasn't difficult.
The anecedata is I see far more people biking year round in Chicago (even in the pretty brutal subzero January/February temps) than I ever can recall.
Granted it's a very flat city without much elevation changes, but there's definitely the spectrum of extreme heat in the summer and extreme cold in winter that doesn't seem to stop anybody
[0] https://chi.streetsblog.org/2024/05/28/cdot-built-it-they-ca...