Tall rider on chinese bike

I'm 190cm and 72kg with most of the height in my legs. So you're pretty much built like me but scaled up. I ride a 58 and have the saddle pushed all the way back, the handlebars all the way up and then some. That is 58 is as small as I can fit. I think on a 58 you will be able to ride just fine on the flat. It may even be pretty aero to have such a tiny bike. BUT, as you raise the saddle it's also moving backards over the rear wheel. The handling will be very compromised going up hill with too much weight backwards leading to the front wheel lifting. You will also have 'exciting' descending with so little weight on the front wheel. You could get speed wobbles starting at pretty low speeds like 55km/h. I would think a 60cm is the absolute smallest bike you should consider. Being tall costs money and unfortunately, you will need a large bike and very strong wheels.

Seat tube length is not a good guide to frame sizing as top tubes slope so differently between models and there is so much height latitude via the seat post. Admittedly you might be at the upper edge of what Chinese companies consider worth manufacturing.

This is why sizing has mostly settled upon stack and reach being key metrics. Stack defines the lowest height of the handlebar, essentially, and reach is important in how far forward the bars will be. I suggest you research what would be a suitable stack and reach for a gravel frame for you then see what's available with those measurements.