Biked is perfectly normal American unless you grew up in Minneapolis. It definitely looks more of a serious activity than going for a bike ride. Cycled would be much considered formal in AE while BE and usually the internationals learn the verb by cycling. I would rather use cycle for climate oscillations or economic ebb and flows.
Dat betekent "we zijn bijna nooit aan het fietsen", niet "we fietsen bijna nooit".
For me "we zijn bijna nooit aan het fietsen" means that only a very small percentage of our time is spent biking / cycling. While "we fietsen bijna nooit" means that there are very few times / instances that we take our bike to go somewhere.
It really is time this bike/cycle thing was sorted out and for "cycle" to be accepted. For the record, I am English and cannot bring myself to use "bike" in this context even if a speaker of American English would do so.To me, "bike" is the thing that I am riding when I cycle to work. Clearly, unless Duo brings itself up to scratch with English English, I am doomed never to complete this module!