Just got the game a few days ago, been playing it quite a bit. The issue is that, in various situations on various stages, I get frame drops as low as the the low 50s and sometimes as low as the low 40s in the worst case scenario. It's strange as, afaik, I pretty much exceed the recommended requirements for the game, and I have seen various YouTube videos of people playing this game with the same gpu and hitting 60+ fps consistently. I have no idea what is going on in my case. Playing the game at 1080p ultra settings mostly.

PC Specs:
CPU: AMD Ryzen R5 1500X
GPU: PowerColor Red Dragon RX 580 8Gb
RAM: 8Gb DDR4 @ 2400Mhz
OS: Windows 10 Pro 64 bit
HDD: Seagate Barracuda 3Tb 7200 RPM
Driver: AMD Radeon Adrenaline Software Ver. 18.10.1

Try lowering volumetric fog to low, make sure you have resolution scale to 100 and you can try temporal AA on/off to see how it impacts your performance. Personaly I have chromatic 'abortion', dof and motion blur off as well but they don't really provide any noticeable performance difference - it's aesthetic choice here. On nvidia cards, multi-res shaders helps with performance with slight picture quality degradation around the edges of the screen.

Imo presets are usually pretty bad (lazy) way of setting your game up. Also if you have vsync on, it might clamp to 45fps if you struggle to maintain <57fps (if 60fps is your target). Mostly I see cpu spikes that tank the fps in my case, esp. when there are too many demons being cut into tiny pieces at the same time + explosions and lots of physics happening with ragdolls all at once (that's what ninjas do, right?). But other than that as long as you have your cpu/gpu boosting properly when needed and not powersaving, you should get a very good performance out of your build.

Edit: Forgot to mention screen space reflections and ssao, those two should be the next big fps killers, but on the other hand ssao increases the image quality considerably. Try screen space reflections off, or even subsurface scattering off to see how it goes. Also general tip I'm sure you know about is that playing in true/dedicated fullscreen increases the performance, compared to windowed/borderless mode.

Yes, but that's when we need the more those fps :/
so I play using the minimum graphic options, the game is still nice.

Yeah that's true... higher fps in fps (or even looter-shooter) is always better ofc and nobody likes to get 1shot in 10fps stutterfest. Game looks pretty great even on low settings, testament to the qualities of wild hog engine no doubt. With some tweaking you can achieve very nice visual quality and good framerates at the same time. That's why I said that choosing automatic preset like ultra is probably not the best idea here, esp. when it gets busy.

Sorry I did not think of this earlier but you can download GPU-Z and it will tell you where the bottleneck is. I have a suspicion it is your memory, not the GPU but do not take my words for it, check it yourself. So you need to have this small program open in the background and set to log then you play a for a minute and pause and go look at the log.