There are also some brief and interesting explanations here.
The meaning is very simple. The division of administrative regions during the Soviet period was an internal matter, therefore it cannot be used as a basis for boundary division after national independence.
To end the dispute between Russia and Ukraine, we must start from reality. The viewpoint that emphasizes Ukraine's sovereignty over Crimea is not helpful for peace.
This stance completely follows Western rules: since the West can demand that Serbs "accept the status quo," the sovereignty of the Crimean issue is also a debatable issue.
The sudden collapse of the Soviet Union resulted in many countries' border issues not being well resolved(This must be attributed to the hasty adjustment of administrative regions during the Soviet era), which was the root cause of military conflicts in many regions.
The most important thing is that the West has already intervened too much in the Taiwan issue, and we need to take the initiative. (Opinions in the comment section)