"Previous constitutions had granted the republics the constitutional right to self-determination, including a right to secede. In the 1974 Constitution, these rights belonged to the "nations of Yugoslavia." At the same time, the constitution included a number of provisions that could deny the right to secede. Article 5 required the consent of all republics and provinces before the borders of Yugoslavia could be altered. Article 283 gave the Yugoslav Assembly the power to determine alterations in the state's boundaries. It was not clearly defined whether unilateral secession was possible or whether this could only be done if the federal government and all of the republics and provinces agreed to it"

At the eighth session of the Central Committee of the League of Communists of Serbia in September 1987, the ideas of Slobodan Milošević won, who energetically and strongly demanded the repeal of the Constitution of 1974 ! Serbia wanted to repeal it! So referencing it is a ludicrous talking point

"The Yugoslav Army (JNA) briefly intervened in Slovenia, but it withdrew after 10 days, effectively confirming Slovenia’s separation. The Serb minority in Croatia declared its own independence from the republic and its desire to join Serbia, sparking violence between armed militias. The JNA intervened in the conflict ostensibly to separate the combatants, but it became quickly apparent that it favored the Croatian-Serbs. [1]

[1]

https://history.state.gov/milestones/1989-1992/breakup-yugoslavia#:~:text=As%20Milosevic%20worked%20to%20consolidate,took%20precedence%20over%20Yugoslav%20law.