This is a recurring pro-Kremlin disinformation narrative about massive restitution claims that Ukrainians will face in case Ukraine joins the EU. In reality, property restitution is not a condition for EU membership and is not on the agenda of EU-Ukrainian relations.
"Restitution is one of the most mythologised issues in Ukrainian politics. Politicians and experts contribute hugely to the belief that European integration will inevitably lead to a review of property rights and many ordinary citizens will lose their homes or have to pay compensation to foreigners, primarily to Poles," Europe Insight analysis reads. It includes an expert opinion that the property restitution issue is "above the EU's competence" and could not be inserted into the EU-Ukraine Association agreement even theoretically.
Read an earlier disinformation case alleging that Poland wants restitution of II Rzeczpospolita from Belarus [Second Polish Republic] property and a total clean-up of the political sphere.