The Soviets never sent humans into the reactor to remove melted core material. The remains of the Chernobyl No. 4 core are still there inside the sarcophagus, and I don’t think anyone was making serious plans to remove them even before the Ukraine war got in the way.
(The job that got so many Soviet workers exposed was moving solid radioactive debris from the exploded core so that the initial containment sarcophagus could be built and the other three reactors on the site restarted. Nothing comparable was required at Fukushima because the explosions there didn’t breach any of the cores, thus no chunks of highly radioactive graphite to shovel off the roofs. I understand that the Soviets did try robots, but radiation isn’t good for electronics and, well, it was Soviet equipment in 1986—they just weren’t very effective.)