Add this code to the Custom CSS field on the Settings tab of your Calculator widget’s settings:
[class*='FormFieldLayout__Hint-sc'] {
opacity: 0 !important;
transition: opacity 0.3s ease-in-out !important;
}
[class*="FormFieldLayout__Container-sc"]:hover [class*='FormFieldLayout__Hint-sc'] {
opacity: 1 !important;
}