Pevensie

I do not think the policy of the US or another country determines whether Taiwan is a country or not.

Since the Russian Federation is using cluster bombs in the war, it is morally acceptable for Ukraine to use them as well. The Union in the American Civil War and the United Kingdom in World War II made similar arguments.

That is not true. The U.S. government did not recognize East Germany until 1974 despite the country, along with the rest of central and eastern Europe, being the epicenter of U.S. foreign policy.

Ending the war in Ukraine is in the U.S.'s interest.  The U.S. is giving Ukraine billions of dollars in military aid. The chances of this war turning into World War III are becoming more likely every day. Many civilians are dying and being displaced.

A reasonable and likely agreement would be Russia being allowed to keep the part of Ukraine it currently controls and agreeing to a cease fire and in exchange Ukraine with its newly drawn border would be given EU and NATO membership.

Can you explain why Taiwan is not a country without mentioning any other country or international organization (e.g. UN, NATO, EU)?

The national debt does not pose any problems as long as USD remains the global reserve currency.

I am not willing to die to defend Turkey, although Turkey is a country. My willingness to die in defense of country does not effect that country's legitimacy. 

The U.S. not officially recognizing Taiwan as a country does not mean Taiwan is not a country (in fact you just referred to Taiwan as a country).

The U.S. not officially recognizing Taiwan as a country does not mean Taiwan is part of the PRC.

Yes, we do sell arms to Taiwan. What is Taiwan then? The U.S. cannot sell arms to nothing.

The United States also does not recognize the PRC's claim to Taiwan. The U.S. has committed to repel any invasion of Taiwan by the PRC.

Source: https://www.bbc.com/news/world-asia-62951347x

First, what do you mean by "China"? If you mean the People's Republic of China, then Taiwan is not China since the the Republic of China is the de facto government of Taiwan. In fact the New York University Law Review states "under international law Taiwan merits recognition as an independent state and as such is already a de facto state."(www.nyulawreview.org/wp-content/uploads/2018/08/NYULawReview-75-2-Carolan.pdf)