I don't think there's a completely standard term. The first thing that went through my mind was "pull cord," even though it does not truly fit the central meaning of "cord." The reason is that you usually raise or lower a blind with some kind of "pull cord." To me, this is a _kind_ of pull cord with an unusual shape. The problems with "belt" and "strap" is that they have vague associations other than shape. A "belt" often forms a closed loop. The belt on a pair of pants does, once the buckle is fastened. The "belts" in machinery, like the fan belt on an automobile, are closed loops. A "strap" often has the function of securing something--like something you would put around a heavy package to keep it closed. Or it often has the function of supporting something--like the "strap" you hang onto in a subway or bus to keep your balance while standing.

I would say 'cord,' especially if it is thin/narrow diameter. 'Belts' are usually flat and 'ropes' are usually much thicker than cords.

I had to do some googling but it seems that a roller shutter is a specialized window covering and its mechanism uses a belt. I had never heard of a roller shutter. Venetian blinds are far more common where I live, and these are always operated by a cord, so that might be why so many are saying cord. (I was going to say cord, as well.) As others said, a belt makes a loop. If the ends are not connected, then it's a strap. If you were in a hardware store, I feel certain the staff would understand belt, strap, or cord if it were clear you were speaking about the shutter.

Even if it has a 'handle' to make it easier to pull, the mechanism still consists of a relatively thin length of fibres, compared to a rope. A strap or belt are usually flat, incorporate a buckle, and are used for securing the object within, for example a suitcase, a shoe, or trousers.

Welcome to the rich and complex world of English. Here is an issue related to synonyms, etymology, geography, misnomers, variations, flexibility and/or laziness. So yep - 'strap', 'cord' and 'belt' will all do for me. It is a belt. It is a cord. It is a strap. I grew up in England with Victorian windows which moved up and down and were held in place by hidden cords tied to counterbalancing weights - and guess what? - we called it a sash window. Is it therefore also a sash? The point is, it doesn't matter, really - as all are in general use and (though some may be preferred in certain videos you watch) the names are for all practical purposes linguistically interchangeable. Some others might have limiting geographical or cultural reasons for applying and sticking with just one word, but the likelihood of it ever being important in this case is moot. As an aside: Unfortunately, (and increasingly) videos on youtube use AI generated voiceovers with terrible errors of pronunciation, syntax, emphasis, etc and the subtitles are often symantically meanigless: Good luck. Teacher Gary