Inflation cause

In Economics 101 the cause for inflation is too much money chasing too few goods. Since 2008 the monetary expansion called quantitative easing along with the current covid spending has caused the money supply to double and yet inflation says at or below 2%. Some say that spending more than you take in will cause inflation but since 2000 the national debt has increased from $5 trillion to $25 trillion and inflation has been 3%. Perhaps the economist were not right and so what causes inflation.