Why would using the $U6$ unemployment rate instead of the traditional unemployment rate almost certainly yield different "appropriate" activist macroeconomic policies?

Unemployment occurs in economics when people are unemployed while actively looking for work. The employment rate is determined as a percentage of the total population of jobless people by the total number of people in the labour force who are currently employed.

In $2012$, the Fed took a middle ground by attaching its interest rate objective to the unemployment rate. As soon as jobless rates were high, the (passive) monetary policy was focused on maintaining the targeted interest rate. However, when the objective was altered as soon as the jobless rate went below that threshold, this became active. The other option was to maintain a level of inflation and unemployment.

Target deflation to stay around a certain level means lower unemployment rate, which limits the interest rate's flexibility. Gross Domestic product cannot rise in the long term, therefore unemployment rate remained at its base rate. A stimulus will boost aggregate demand, raise inflation by a full percentage point, and have no effect on the unemployment rate. Because the unemployment rate remains steady, the Fed does not need to reduce its support.