While the Soviet Economy did begin to stagnate towards the end of the Soviet Union's lifespan, it did not collapse due to economic failure. The economic collapse happened right after the USSR was dissolved, leading to spikes in poverty, food insecurity, a loss in healthcare, and an estimated 7 million excess deaths. The reasons the USSR collapsed were more nuanced than simply saying the Soviet Model "didn't work," because fundamentally it did, and it worked quite well for most of its existence. Stephen Gowens' essay Do Publicly Owned, Planned Economies Work? goes into detail on what legitimately worked quite well, and where it started to falter and eventually was dissolved from the top-down.

The reasons included the following problems:

Liberal reforms that gave the Bourgeoisie power over key industries (such reforms were actually a major desire of the 1968 Dubcek platform, in even greater quantity, hence why it was shut down by neighboring Warsaw Pact countries)
A firm dedication to planning by hand even as the economy grew more complex and computers too slow to be adapted to the planning mechanisms
A huge portion of resources were spent on maintaining millitary parity with the US in order to dissuade US invasion
80% of the combat done in World War II was on the Eastern Front, and 20 million Soviets lost their lives, with no real economic support from the West in rebuilding despite taking the largest cost of war
An enclosed, heavily sanctioned economy relied on internal resource gathering, closed off from the world market

Countries like the PRC have taken to heart what happened in the USSR. As an example, the PRC shifted to a more classically Marxist economy, focusing on public ownership of only the large firms and key industries, and relying on markets to develop out of private ownership. This keeps them in touch with the global economy without giving the bourgeoisie control of key industries, and thus the bourgeoisie has no power over the economy or the state.

Moreover, as a consequence of collapse, polling from Pew Researcg suggests 77% of Czechs believe they are worse off economically than under Socialism. This is generally true in various degrees across the other post-Soviet states, had the USSR not been dissolved, it would have likely continued to improve conditions at a faster rate than modern Capitalism, and the misery it has brought.