The Guardian published a report that it seems that many Ukrainians whose first language is Russian are trying to change the language they use most often to Ukrainian. The article can be found at https://www.theguardian.com/world/2023/apr/24/russian-speaking-ukrainians-want-to-shed-language-of-the-oppressor
There are interesting comments about how Russian had been seen as the language of the city of Kharkiv/Kharkov and how Ukrainian speaking people from the countryside had faced stigma and had often switched to Russian.
There seems to have been a dramatic increase in the use of Ukrainian in formerly Russian speaking areas. This has not happened suddenly and one speaker says she decided to use Ukrainian more after 2014 but this change has become more marked since last year's invasion.
One person in the article referred to Russian as a lingua franca and presumably it still could be if there become more contacts with other countries that used to be part of the Soviet Union. It will be interesting to see whether people in Ukraine continue to learn and speak Russian because of its instrumental usefulness or focus even more on languages like English and German.