Anyone who has ever visited a plenary session of parliament (as I have as part of school trips) knows that they are unbelievably boring. 99% of the time, they aren’t about cutting edge law making that will propel society into the next century, but about routine declarations or posturing where a politician wants to promote the local industry.
It is IMO completely acceptable for attendees to just be there and do something else, while waiting for a topic that interests them. This is no different than zoning out during some group meetings where you don’t really care and don’t need to know about most of the topics, but you still are present in case your input is required.
That said, I understand your concern if your definition of work for an elected official seems to be “staring aimlessly at a podium during a plenary session.”
And before you say: “they should actively participate!” Good luck doing that in a session with 200+ participants. Law making is done in smaller sessions and committees. The plenary session is a formality.
In this particular case, chances are that they were filming during “het vragenuurtje”, the Q&A where Flemish members of parliament can get answers from ministers to submitted questions. It’s completely normal for one member to sit at attention while their question get answered while others sit and wait for their turn, and do something else. After all, that member may have an interest in the lack of highway signalization to his village, while other members don’t care. (Yes, Flanders is small enough for these kind of things to be brought up in parlement.)
I totally understand that this doesn’t fit the standard narrative of the lazy politician who doesn’t work for my money, and for that I’m sorry.