Government portals, job boards and exam sites almost never ask for a smaller photo. They ask for one under a specific number of kilobytes, and they refuse everything above it.
There is no fixed relationship between a quality setting and a file size. The setting that takes a plain headshot to 60 KB will leave a busy outdoor photo at 400 KB, because compression works by throwing away detail and one of those pictures has far more detail to throw away.
That is why the usual advice, set quality to about 70 and see, turns into a loop of export, check, adjust, export again. Working backwards from the number instead removes the guessing entirely: the limit is the input, and the quality is whatever satisfies it.
When the limit is very small, quality eventually stops helping and starts producing a smeared mess. At that point fewer pixels beat lower quality, and a photo that has been scaled down and kept sharp looks far better than one held at full size and crushed. You are told when that happens rather than being handed a ruined picture.
Image encoders cannot be told to produce an exact byte count. What matters is landing under the number the form checks, which is what this does.
Yes. Set 50 KB as the limit and tick the minimum box with 20 KB, and it stops as soon as the file is inside the range.
No, not for a size target. PNG compression is lossless so there is no quality to trade away. Forms almost always want JPG anyway.
No. The work happens inside this tab on your own device.