Is it possible to return to Ukraine without a valid travel document (e.g. only with an internal passport or birth certificate in the case of a child)?
As a rule, in accordance with the Act on Foreigners and the Schengen Code, a foreigner crossing the border is required to have a valid travel document.
Although in practice we do not observe any problems with the Polish border guard in such a case, it is worth obtaining the relevant documents from the Ukrainian embassy before departure.
Another question is whether the expiry of the validity of a passport deprives its holder of the right to enter the territory of Ukraine – this question, however, concerns the provisions of Ukrainian law, not Polish, and a practice that may currently be different than the regulations.