Germany lost the first world war and had very high and quite sudden war debts plus suddenly had to pay reparations amounting to about 25% of GDP, denominated in foreign currency - this is important. Germany then printed money (this is similar to today) and bought foreign currency in the FX markets, at essentially any price available (this is not). The money flowed to the war winners, out of the domestic economy. This caused instant and quite strong devaluation of the German currency.

What the US does: It invests a comparatively tiny amount of money (~$2 trillion, <4% of GDP) into the local economy, where it will cause actual economic action (people buying things and services), to make up for lack of demand caused by Covid. FX markets are not touched. AFAIK it is aiming to finance at least a part of this through taxation.