How to block DC of triangle waveform from 555 powered by single supply?
C7 and R5 make an RC high pass filter with a cutoff frequency of .16 Hz and an RC time constant of ~1s. In order to have no DC offset, the capacitor must charge which takes \$5\tau\$ to reach 99% charge, or 5 seconds in your case.

To see the removal of the DC offset, you either need to simulate your circuit for 5s, or use a filter with a higher cutoff frequency. Since it looks like your circuit has an output frequency of ~200 kHz, a .16 Hz high pass filter is not really suitable (and probably wouldn't work well with an electrolytic cap), and you really should use a filter with a much higher cutoff frequency, say 20 kHz.