In my kitchen mixer tap the cold water pressure has been considerably lower than normal for a few days. The hot water is fine. (The pressure from the mains tap is normal.)
I don't know if the end of the tap comes off for cleaning. I don't want to force it and damage the tap!
As it's a mixer and you say the hot water pressure is fine, then your problem is not in the nozzle at the end of the tap.
Turn the cold supply off and remove the head of the cold tap to allow inspection.
It may well be a washer problem.. they do sometimes break up or become dislodged.
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