Marxist economics doesn’t propose complete enforced equality. It fundamentally proposes a more democratic economy in which control is switched from capitalists to the workers. While this would result in a more equal economic distribution, this would mean, in terms of marginal utility extracted from wealth, that the same money would be used more efficiently. While the incentive may be less, this will be because it is easier to make people happier and healthier for less overall resource usage. Having to work less of your life away to live comfortably isn’t a bad thing. The artificial scarcity enforced by capitalism has conditioned us to think that raw wealth generation is the only way to improve living conditions, while in reality distributing wealth on a more equal and need based basis can do so as well. Even so, incentive is not destroyed, and there isn’t absolute equality.
Fundamentally, the need to work to generate resources will still exist, and individuals could still be rewarded for their personal labor. Socialism itself doesn’t seek to create complete equality, and as we’ve seen with social democracies, redistribution of wealth to help meet basic needs doesn’t drastically reduce incentive.