It doesn't necessarily have to be equivalent to 'P'.
If your camera has a through-the-lens meter, then Shutter-priority or Aperture-priority auto-exposure mode, or Program mode, or metered-Manual mode all use a reflected-light meter reading.
In a Program mode, cameras often have a program-shift function, where you can use the program, but bias it to favour a fast shutter at the expense of aperture more than the default program would; or the opposite, favouring stopping down at the expense of a slower shutter.
Then there's more variation available in how a TTL reflected-light reading is distributed across the frame: spot, centre-weighted average, etc.
I remember there being an accessory you could buy that's a diffuser-dome to fit the front of a standard lens, that even allows you to use the TTL meter for incident-light readings (fit the dome, and point the camera away from your scene, toward the light, to meter before taking your photo in manual). I think it must have been the 80s when I saw that. I never bought one.
Not all cameras have a through-the-lens meter. In some the meter cell just looks forwards off the face of the camera. That's still a reflected-light reading, unless it has a diffuser attachment for incident readings.
All of them, plus.
I, and others have, used a plain white Styrofoam coffee cup (new) to turn camera and, in general, spot meters, into incidental machines, when used in the same fashion as normal incidental meters.*
Pieces of nails normal plate centers of styrofoam can be easily pressed into form fitting disks, and placed in Series filter holders or even in a lens hood, to get incidental readings and, as pre'flashing' filters for dim shadowed scenes for paper negatives and films.
My regular meter kit, includes a Pentax V spot meter, Gossen Luna Pro F, and Master V meters, which are small and have inverted proprietary "cone" domes, which can be used in Master IV meters.
I still have 4"x5" polaroid, about 40 sheets, to test with and a Canon G10 to preview shots in b&w or monotone, as you like.
*The camera lenses should be set to infinite, to be out of focus and the apature wide open, for fast adjustments, in camera, my preference.
Of course you can directly read just the meter at the F stop/Shutter Speed, if you desire