While no country officially calls it uncapped money printing, both China and Vietnam operate systems of massive state directed credit creation as an alternative to capitalist monetary policy. Instead of relying on private banks to originate loans for stock buybacks or real estate speculation they use publicly owned banking sectors to directly fund state owned enterprises and massive infrastructure projects. They are effectively using currency issuance as a tool for allocating real material resources and labor.

Their approach relies heavily on what Western economists complain about as financial repression. Keeping interest rates low allows the state to guarantee cheap credit for massive development projects that benefit the broader society. If the capital account were fully open the domestic elite and foreign investors would immediately move their wealth offshore seeking higher parasitic yields in Western financial markets. Such a massive capital flight would trigger the scenario you described where everyone dumps the local currency causing it to plummet in the foreign exchange market leading to imported inflation that crushes the working class.

China and Vietnam learned from the 1997 Asian Financial Crisis when countries with open capital accounts were completely destroyed by Western speculative attacks. Strictly controlling the flow of capital across their borders forces domestic wealth to remain inside the country where it can be put to productive use rather than fleeing to Wall Street casinos. That's the mechanism that allows them to maintain sovereign control over their macroeconomic policy and prioritize long term industrial development over the short term profit demands of international speculators. Basically, you cannot have a stable currency independent monetary policy and free capital flows all at the same time. So, a socialist oriented state must sacrifice the free movement of capital to protect its economic sovereignty.