The tiny squash fruit on my very healthy looking summer squash plants are shriveling at the blossom end. They are not black spots, rather the small zucchinis are just shriveling. Plants are deeply mulched. Leaves are big and healthy looking in raised beds. Stems look sturdy.
Small Squash Fruit Shriveling
Certified GKH Gardening Expert
It is a pollination issue. These articles will help: