If you want to sort by severity and not total events, try this:
index=pvs | chart count(eval(PVS_risk="CRITICAL")) AS CRITICAL , count(eval(PVS_risk="HIGH")) AS HIGH, count(eval(PVS_risk="MEDIUM")) AS MEDIUM, count(eval(PVS_risk="LOW")) AS LOW, count(eval(PVS_risk="INFO")) AS INFO, count(eval(PVS_risk="NONE")) AS NONE by src | sort 10 - CRITICAL,HIGH,MEDIUM,LOW,INFO
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