I had a Ukrainian friend and I thought he'd told me that Russian was strongly encouraged. I thought the state had a stronger policy towards making sure everyone spoke russian.
I just looked it up and it appears that wasn't something the USSR ever really did.
It was "strongly encouraged" in the way that English is "strongly encouraged" in any US company. 3/4 of the company can speak Hindi but in all hands meeting everyone speaks English because it's the only language that everyone in the room understands and speaks (poorly, lol).
It would have been the normal thing to do. But the USSR went the other way because it was committed to the idea of being several separate soviet republics, so it pushed the idea of Ukrainian language and culture as something distinct from Russian in order to present the idea of a Soviet Ukrainian Republic as something distinct from the Soviet Russian Republic.