Don't know about Belgium, but there are no Dutch regulations requiring showers in office buildings[1], unless the work environment is exceptionally warm, dirty or involves dangerous chemical/biological products.

The average (non-electric) city bike speed here is probably around 10-15km/h, which makes a bike commute not any more strenuous than a literal walk (not jog) in the park. Nobody here expects people to shower after a walk. Of course it also helps that the country is very flat, the climate is mild, and cities are compact.

[1] https://www.wolterskluwer.com/nl-be/expert-insights/as-a-cli...