What should I do in a case where the last night for קידוש לבנה is cloudy?
If the moon is not visible you may not recite it. It needs to be visible at least partially to the extent that it actually shines through the clouds, and you can appreciate its presence by seeing things to its light.
Some maintain not to recite the Bracha even if there’s a thin cloud, but one should not be stringent if this is the last night.
See more here:
There might be however a possibility to rely on opinions that the last day is later. See here for details:
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