I think asking this question on a Lemmy.world community is a bit of a mistake. If you want an answer from Marxists, it would be better to ask it on an instance with more Marxists. As a consequence, there are numerous errors people have been making here that are a consequence of not really engaging with Marxist theory outside of Wikipedia definitions, the oversimplification of which has led to drastic errors in conclusions, the blind leading the blind.
Communism, for Marxists, would look like a Worldwide Republic with full Public Ownership and Central Planning. The issue you are runnung into is Marxist definition of the State. For Marxists, the State is an instrument of Class oppression. When you eliminate Classes, you so eliminate the State. Administration, planning, legal networks, etc would still exist without what Marx considered a "State" to be. Moreover, this is the fundamental difference between what Marxists want and what Anarchists want. From Engels, in Socialism: Utopian and Scientific:
The first act in which the state really comes forward as the representative of the whole of society -- the taking possession of the means of production in the name of society -- is at the same time its last independent act as a state. The interference of the state power in social relations becomes superfluous in one sphere after another, and then dies away of itself. The government of persons is replaced by the administration of things and the direction of the processes of production. The state is not "abolished", it withers away. It is by this that one must evaluate the phrase "a free people's state" with respect both to its temporary agitational justification and to its ultimate scientific inadequacy, and it is by this that we must also evaluate the demand of the so-called anarchists that the state should be abolished overnight.
The reason it isn't instantaneous is because Marx and Engels believed Private Property could only truly be folded into the Public Sector once it had developed enough to be easily planned, and this happens at different rates across different industries, and to different degrees. The revolutionary aspect is still necessary and quite short-term, but once the Proletariat has siezed control the productive forces must be developed within the constraints of physical reality, ie you can't will the system or decree it into being fully publicly owned and centrally planned. It's a gradual process, but revolution is required up front because without it the Bourgeoisie maintain political power, and they need that power wrested from them before Socialism can even begin.
I highly recommend checking out my Introductory Marxist Reading List if you want to learn more, but feel free to ask any questions!