Oh dear I wish it was true, but it isn't. Eastern Europe is facing a dramatic brain drain and it isn't slowing down. For instance, Romania has lost 15% of its population in the past 30 years (3.5M people!), most of the loss coming after 2000 and the decline being pretty much constant between 2000 and today. Czech Republic and Slovakia are the only country in the region with a growing population (a few percent in 30 years, even the aging Germany looks dynamic by comparison), and Poland is stagnating. Evey other country is losing population every year.[1] This is an ongoing demographic catastrophe for these countries.
[1]: https://www.monde-diplomatique.fr/cartes/fractures-est-ouest (In French, and the infographics is paywalled, but you can access an animated gif by right clicking on the image and opening it in a new tab)