wyznaczon
Wyznaczon is a form that appears in relation to the Polish verb wyznaczyć (to designate, to appoint, to determine). In standard contemporary Polish, the past participle used as an adjective is wyznaczony for masculine singular, wyznaczona for feminine, and wyznaczone for neuter or plural. The form wyznaczon is not a standard or widely accepted standalone form in contemporary grammar. It is generally not listed as a separate lemma in major dictionaries and is more likely to be encountered as a nonstandard, dialectal variant, a typographical error, or as part of a proper name in specific texts.
Because wyznaczon is not typical in modern Polish, most authors would prefer the standard forms wyznaczony/wyznaczona/wyznaczone
Correct standard usage: wyznaczony termin (designated deadline), wyznaczona osoba (designated person), wyznaczone miejsce (designated place).
If a text shows wyznaczon, it is advisable to look for the intended standard form or consider
Wyznaczyć, wyznaczony, wyznaczone, designation, appointment.