I have cycled every working day in The Netherlands and in Germany for years (in Germany it was 22km per day) and I would often cycle a bit recreationally in the weekends. It really isn't an issue at all. I just have a waterproof jacket (one of those that circulate air as well), water resistant shoes, and rain pants. On very rainy days, I would put on the rain pants and would arrive mostly dry.

It is not really an issue.

The only thing that was slightly meh was the yearly ~two weeks of thick snow in Southern Germany. It increases effort a bit, but still not a huge issue and the cycling roads got cleared pretty quickly.