During the interrogation even they're barely visible. You can see them in screen caps
While normally we're on the same wavelength about figures, I do feel the socks and suspenders are a detail that shouldn't be missed/overlooked. Like haytil said, sure they're not visible but it's a nice detail to be like "oh hey look, they actually add the suspenders" like it was for the DX01
No offense towards Kato, but you'd think a tailor of his caliber would be able to include suspenders. Maybe there weren't enough reference shots for him to make them accurate or maybe there was an agreement in that thread to not include suspenders, but it surprises me that none were made for his suit set and would surprise me again if Ht decide to not include them here