Indeed, and it should always be remembered that the only reason there are Russian speakers in Donbas is that the Soviet Union moved them there after all the Ukrainians starved to death.
A bit more complicated than that.
The region later named Donbas had been multi-ethnic ever since Ukrainians, Russians, Greeks, Jews, Germans and others settled there, mostly as peasants, in addition to native Cossacks.
Lots of Russians moved there in the mid to late 1800s, when coal stated to get exploited at industrial scale, and they dominated the new and growing cities, while the countryside remained more Ukrainian.
Ukrainian peasants also moved to the Donbas cities, where they were a minority and tended to get assimilated, vs the other way round. So that's how Russian language rose to rival Ukrainian.
Holodomor was, in a nutshell, a war of cities against the rural countryside and thus affected Ukrainians disproportionally. (Don't forget that Russia, too, had suffered unspeakably severe famines since WW1; just as an aside)
WW2 and Nazi Germany's deportations and massacers further depopulated the area (as the enire area of Ukraine). This probably affected Russians and Ukrainians roughly in similar prportions
After WW2, the industries of the Donbas were one again repopulated - from all sides, but Russians were probably a majority of new arrivals.
Once again, ethnic Ukrainians would more likely assimilate to Russian language there than vice versa.
So that's how come Russian is spoken more in Donbas than Ukrainian.
And still, half of the Donbas population, at least prior to the ongoing genocide, identified as Ukrainian, a majority was happy to secede from the USSR and, implicitly, Russia.
