Force that drive the dollar up, and forces that drive the dollar down. Its not as simple as some YouTube videos might want you to think.
What drives the dollar up?
First is demand. When you need the currency to buy something, that need produces the demand. The reason why the US dollar has not fallen despite the massive printing, is that people need every cent and dollar to keep the roof over their heads, gas for their cars and food for their bellies. The basic necessities.
Second is the velocity of money. This is the money in actual circulation. You can print much money, but if the money is locked up in the banks or in stocks, and not moving within the economy, where it may not reach the people at all, you still get the effect where you don't have enough money.
Third is what you can purchase with the dollar. So long as the dollar is being used to purchase something, whether its Saudi oil, soybeans from Brazil or coal from Australia, there is value behind the dollar.
Fourth is that expanding economy and productivity absorbs the excess dollars in the market.
These factors swing it back and forth.
There is interest rates. People will invest in dollar denominated assets for the interest. Also relates to the first. Higher interest rates makes the dollar go up, and lowering them makes it go down.
When the dollar is exported out of the US economy via trade, this reduces the dollar circulating within the US domestic system. However the dollar supply increases within the global economy. Life the fifth, this is double edged and swing one way or another.
There is the perceived value. As long as the US dollar has good perception, it has value. But if people are flocking to gold, silver, other assets, foreign currencies, bitcoin and other crypto in reaction to a decreasing perception of the US dollar, the US dollar will lose value with increased supply and reduced demand.
What drives the dollar down?
Excess supply in relation to supply. If you have too much cash and not enough goods and services, excess cash competes with one another and that rises the prices of goods. Inflation goes higher which in effect, reduces the value of the dollar.
Contracting economy and productivity. This relates to the above.
Less things to export from the US. US dollar buys things that are exported from the US. If the US offers less attractive things to purchase, ranging from Boeing to chips to iPhones to soybeans and oil, there is less demand for the US dollar to buy these things.
Less incentive to invest or purchase assets in the US. Buying US real estate, investing in US bonds, US company stock create demand for US dollar. If these things are less attractive to the investor, there is less demand for the US dollars to purchase these things.
Excess dollar supply versus local currencies. Even if the US dollar is the reserve currency, you need local currency for your day to day needs. Thus businesses and banks need to convert US dollars gained from exports, FDI and offshore labor to local currency. This creates competition for local currency. If there is not enough local currency that is printed, the local currency will go up while dollars will go down.
Interest rates. Low interest rates will drive the US dollar down. Higher interest rates with major foreign currencies can also have this effect.
You have all these factors and forces exerting active, reactive and counter reactive influences on each other, till you begin to tip the scales to another direction.
Case of Japan doing QE with massive printing of Yen and yet it has low inflation to deflation, and the currency not going Weimar on you. The Japanese case is often brought about by Modern Monetary Theorists that you can print indefinitely and not something bad happening to you at all. You can counter this because Japan has an export surplus most of the time, and that its products are highly sought after. This produces value behind the Japanese Yen.
The problem of QE however, and of low to negative interest rates, is that zombie companies---companies that are no longer competitive and unable to pay off their loans, even much of their interest due---can continue to borrow cheap loans to stay afloat. With zombie companies all over the place, the country becomes filled with uncompetitive companies, with less new entrepreneurial growth and with that comes innovation. Massive printing and QE is having that effect on US companies now.