Identifying flying insect from southern Poland / Upper Silesia area
Found it, with a lot of help from my local neighbors. It is Melolontha melolontha or cockchafer.

From English Wikipedia:

The cockchafer, colloquially called May bug or doodlebug is a European beetle of the genus Melolontha, in the family Scarabaeidae.
Once abundant throughout Europe and a major pest in the periodical years of &quot;mass flight&quot;, it had been nearly eradicated in the middle of the 20th century through extensive use of pesticides and has even been locally exterminated in many regions. However, since an increase in regulation of pest control beginning in the 1980s, its numbers have started to grow again.

Here, where I spotted this insect (Upper Silesia) it is called in local language (in Silesian language) &quot;julik&quot;, which is quite correct, since they seems to appear in July.
However, as per above cited part and as per Polish counterpart to above cited article, officially this insect is called after May, either &quot;May bug&quot; (English) or &quot;Chrabąszcz majowy&quot; (Polish). Most likely because adult forms of this species appears mature by the end of April and through May.