According to the moment.js docs, the standard way to get the difference between two dates in your example would be now.diff(date, 'months', true), which should return a floating point number greater than 6.

now.diff(date) returns the millisecond difference between those two points in time. Calling moment.duration({milliseconds}).asMonths() is not ideal because some months may be 30 days long and others may be 31 days long. It appears that moment.js uses somewhere in between 30 and 31 days as the duration of one month. To address this issue, moment.js have discussed calendar diffs in the docs:

moment#diff has some special handling for month and year diffs. It is optimized to ensure that two months with the same date are always a whole number apart.

So Jan 15 to Feb 15 should be exactly 1 month.

Feb 28 to Mar 28 should be exactly 1 month.

Feb 28 2011 to Feb 28 2012 should be exactly 1 year.

The definition of "a month" can only be a "fuzzy" one, as the months of the calendar are of different lengths. One way of defining it would be to divide the year into 12 equal parts and use that as a "month-metric":

function monthsUntil(year,month,day,hour=0){
 const trg=new Date(year,month-1,day,hour,0,0), 
  now=new Date(), nxt=new Date();
 nxt.setFullYear(nxt.getFullYear()+1);
 return (12*(trg-now)/(nxt-now)).toFixed(4);
}

console.log(monthsUntil(2022,12,1,16))