@grudas
56cm is too big for 5ft 9. 80mm on that size frame just isn't nice handling wise. 90mm even is borderline. Just too fast and twitchy. It's one of those things where you would need to test a 54 with a slightly longer stem to feel the difference. Your legs are about average for height, a fraction over perhaps. In the cycling world, perhaps slightly under though. You'll possibly get away with slightly racier geometry and some spacers as a result. It looks like the bike shown requires +25mm with the integrated setup minimum. You'll turn the pedals fine at 170mm/80cm. You won't know any different. They just won't be 'right' for you and neither will the saddle be in the very small ideal fit window as a result - I believe this to be only a few mm wide. The less the volume and intensity, the more you'll get away with it. In an ideal world, from pedal turn 1, they'd be shorter. 165mm at 80cm should be safe.
The bike you are looking at isn't even labelled properly by Sigma. Never trust 3rd party sites for geo. It's a 51.9 TT and Argon 18 themselves label it an XS. The bike labelled XS by Sigma is in fact the XXS. Your size would be the Small at 53.9 TT which Sigma labels a Medium. If that doesn't work for you, different bike.
https://www.argon18.com/en/bikes/road/gallium-cs-disc/sram-rival-etap-axs
I also wouldn't trust chat gpt - the stack figure above is wrong for a start at 550mm. No size has 550mm. On the 53.9, it's 538mm and 561mm with the system. Those measurements aren't from the small size on chat gpt. They're from the XS. The reach is 384mm, again 377mm is from the XS (51.9TT). If you start looking at the tables yourself, you'll see what is race like and what is more relaxed for your size around 54.
Chatgpt also has no idea on the bar reach. These can vary typically between 70mm-80mm. Some bikes have a slightly short reach even though they may be 'race' bikes as they now purposely do so to fit a long reach integrated bar setup that makes up for the difference for example. If you aren't then aware, that's a whole new integrated bar setup and perhaps the handling you never wanted.
The bar on the Argon 18 is short at 70mm -
https://shop.fullspeedahead.com/en/handlebars/road/vero-compact-alloy-handlebar
Nothing listed for Vitus compact bars.
Edit - Noticed you've seen the disparity between sites, but chatgpt measurements are still wrong.