Based on the image, it looks like a default phone browser with a reader mode icon on the right side of the URL box it also looks like IOS browser.
That user interface looks nothing like iOS, though. It's more an Android OS. Probably by Samsung or OnePlus
Many browsers on mobile especially on android don't have dark mode and for some the dark mode is pretty messed up. Chrome for example is a very common and popular browser on mobile and it doesn't have a very responsive dark mode. Fun thing is I for some reason just prefer this forum in light theme.
What are you still doing with chrome? Use Firefox for android and install Dark reader. You will thank me later

Infact I think this is the longest place I surf on light mode because I use dark mode most of the time outside the forum, well I guess photochromic glasses cover for that.
Even the default night light filters for Windows and Linux can be very helpful. I can spend so many hours on PC with the blue light filter on. I can't spend more than 10 minutes on my PC minus my eyes hurting when I turn it off.