[NVI]

If your monitor doesn't cover the entirety of P3, it does "degrade" to the closest color your monitor is capable of showing. This isn't necessary sRGB — most monitors that don't fully support P3 yet still support gamuts wider than sRGB.

I don't know whether relative or perceptual colorimetric rendering intent is used.

You can open https://codepen.io/NV/pen/XLOOdE in Safari Technology Preview and check how it looks on various monitors.

[teilo]

There is no such thing as a monitor degrading. The monitor displays the color values it receives, period. It does not do profile conversion. It does not know anything about rendering intent. It doesn't even know about color profiles. It knows: Display this RGB value for this pixel. That's it.

It is up to the software driving the display to choose appropriate color values. That means that if a monitor has the Display-P3 gamut, then it is up to the OS or browser to know this, and send appropriate color values when viewing sRBG data such that the colors are not oversaturated.

Yes, graphics cards can store LUT tables to linearize the RGB curves to neutralize grays. But this is not gamut mapping. Profiling is a process that happens after a display is linearized, and that profile is loaded into the OS.

I'm in the color print industry. I know color management intimately.