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We tend to have quite a few squash that go this way. Normally assume it is due to them not being pollinated particularly well, and the plant drops it to favour the next one along on the vine.
Have you had any fruit develop past this stage?
My partner is a fan of pollinating squash by hand. Find a male flower that has opened recently and has plenty of pollen on it, snap it off the plant, strip the outside off to expose the anthers, then wipe it all over the centre of the female flower (with the fruit behind it).
https://www.vegetariantimes.com/life-garden/how-to-hand-pollinate-squash/
I find this method a bit explicit and leave it to the bees.
Any idea what's happening to my squash? I've had a few trombetta and courgettes do this where the fruit starts to develop and then yellows and start to rot from the flower end. This one is grown in a pot, but the courgettes in the ground are similar.