What happened in Crimea? Who can explain it to me in detail?

In the 1920s, the then Soviet Russian Jews borrowed15 million dollars and promised to sell Crimea to Jews as a debt repayment. But then the Soviet Union regretted it and didn't want to give Crimea to the Jews. 1954 after the loan expired, Khrushchev discovered the loophole in the agreement to sell Crimea that year: Russia sold Crimea to Jews. If Crimea is allocated to Ukraine, Crimea will not belong to Russia, and the agreement of that year will be invalid. So the Soviet Union defaulted. Of course, at that time, no one would have thought that there would be a conflict between Russia and Ukraine today.

First of all, after Crimea was transferred to Ukraine, it enjoyed a high degree of autonomy and had its own parliament and prime minister. However, Ukraine has troops stationed in Crimea and has actual control over Crimea. What you said is similar to Hong Kong and Macao autonomous regions, but it is not a provincial administrative unit and should belong to a federal autonomous country. For example, Mongolia decided to join China by referendum (though it is impossible). After joining China, they still have a high degree of autonomy, political and economic autonomy, and even can keep their own army, but they should abide by China's restraint in diplomatic and foreign military deployment. I wonder if this metaphor can be understood.