slow flush/drain toilet when ... help

hello ,, i'm new to this complex from 14 floors and i'm in the 1st floor flat


i have this problem in the toilet When flushing "soft things" it has no problem

but when flushing "solid things" after , flushing be slow and slow draining ,Water Level Raises and sometimes it bring back little air gurgles after the slow draining but not overflow ........... // After 20 flushings maybe the toilet flushing system back to normal no slow drain/flush


how i fix this problem

/ my main language is not english i hope its understandable


thankS