Exposure = Illuminance * Time (this is the definition of the term)
Illuminance is controlled by F-stop (really T-stop) and scene illumination.
Therefore, by definition, exposure is controlled by scene illumination, as well as by two other things.
This is not open to debate. It's the definition of the term that most, if not all people agree upon.
Adobe: "Exposure is the amount of light that reaches your cameraβs sensor,..."
Wikipedia: "In photography, exposure is the amount of light per unit area (the image plane's illuminance times the exposure time) reaching a frame of photographic film or the surface of an electronic image sensor, as determined by shutter speed, lens F-number, and scene luminance."
Photographylife: "In photography, exposure is the amount of light which reaches your camera sensor or film."
Masterclass: "Camera exposure is ... the amount of light that reaches the film or camera sensor when a picture is being taken."
SLR Lounge: "Exposure is the amount of light a sensor (or piece of film) receives."
No-one is disputing iso sets the target exposure* to output the image lightness the camera is calibrated to for the iso setting.
But iso can have no effect on exposure* at all in manual mode as long as highlights are not clipped. I have posted many examples where that is the case
The meaning of amount of light and how to give it a value has been explained countless times in other threads by at least Bob and many others. I am sure you can find the posts if you need to refresh your memory.
You are still running away from posting the definition of scene luminance and exposure as you used them in your thread title as you always do when you have backed yourself into a corner.
You are using different definitions of those terms while trying to prop up the false statement in your thread title and so are continuing to go round in circles π
* exposure - amount of light that struck the sensor per unit area while the shutter was open
Weird that this site and others talk about "ISO" as if it were a measurable variable complete with units of measure, placing it on a level with the almighty triumvirate of aperture f/number, scene luminance and integration time (shutter period).
At the risk of boring y'all, on one of my cameras, ISO does nothing to the raw at all. Nothing. Zip. Nada.
With regards to total light, photons, or, equivalently, lumen seconds (luminous energy). With regards to exposure, photons/area, or, equivalently, lux seconds (luminous energy / area).
So, now it all makes sense to you, right? πππ
Let's take it down a notch -- more light, less noisy photos. But also, more light, greater amount/risk of blown highlights. Also, to get more light, we have to either use a wider aperture, resulting in a more shallow DOF, a longer exposure time, which increases the risk/amount of motion blur, and/or add in artificial light, which changes the lighting of the scene.
Can't technology and/or software make up for less light? To an extent, yes. I mean, if you're well within the "operating envelope" of a system, then if you're off a stop from the "ideal exposure", it's not going to make that much of a difference. But when you're near the edges of the "operating envelope", being off a stop can be a big deal. So, the more you're near the extremes, the more important this stuff is.