Why did the layout go on a mobile device?

Question

HTML

Guys, this is the first time I've encountered this.
There is a mobile device with a resolution of 1280x800, 188dpi I
designed a non-adaptive page for it, specifically for this resolution.
I assigned the width of 1280 to the container, placed all the elements there.
In the browser and in DevTools in the specific 1280x800 mode, everything is displayed as it should.
On the device itself, I open it in the browser and my float elements do not fit into a row, they are transferred to another line.
That is, as if the screen size of the device is smaller than it is written in the specification ... but it should not be like this.
Maybe something is wrong in the head?
now here is what i have in the code

<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />

Answer 1

1) the browser on the device can ruin everything;
2) whether all prefixes are spelled out;
3) layout using flexbox;