After work I prefer mostly less demanding activities: reading books, playing games, learning from video courses or doing whatever sport is available in the current space-time: riding a bike or a longboard, working out, running, diving, swimming, etc.

Are hobbies in decline ... ? Well, they could be if everyone uses most of their brain cycles "consuming content" online. It is quite absorbing and may result in less interest in hobbies that require higher attention.