Can people who came to Poland after February 24, received PESEL for Ukrainian citizens and their visa-free period has expired, to travel to EU countries and return to Poland?

Provided you have a UKR PESEL and have access to the mObywatel app, you can obtain an electronic residence permit On the basis of this document, it is possible to travel within the Schengen area for 90 days in any 180-day period, provided you have a valid travel document. 

However, if you do not have a electronic document and you wish to travel to another EU country, once you have used your visa-free travel, you must meet the entry conditions set by the authorities of that country. For this purpose, it is best to consult your planned trip with the consular representation.