It's interesting, I asked ChatGPT about this and it said it was not banned, then I turned on "search the web" and it says it was - citing AP News and VoA, basically this very article. I wonder if there's any more info.

Edit: funnily enough DeepSeek gives an answer that sounds plausible: apparently during the Stalinist period of 40s-50s while it supposedly wasn't outright banned "overt displays of national pride were often discouraged" ... That seems to fit, and a bit of judgement over whether something is banned explicitly or simply so unthinkable in the official climate that it may as well be banned.