Both have NVIDIA graphics cards and Intel integrated graphics. This query pertains to any Linux distro.

If the BIOS setup screen is set to Hybrid Graphics mode, not Discrete only, and the distro has only the Intel graphics drivers installed, no Nouveau, no Nvidia proprietary software, will a boot automatically default to the Intel graphics and display everything properly whether console or GUI (Gnome, KDE, XFCE, ...)?

If it will completely ignore the NVIDIA card, will it leave that card in an unpowered or minimal powered state?

My interest is related to possibly acquiring one of these laptops for its superior CPU speed while not being concerned with the graphics drivers. Please note that there is no explicit way to select Intel graphics only from the BIOS setup menu.

Any other relevant comments would be appreciated.

Note I own no Optimus hardware, and couldn't answer anyway because of knowing nothing about the specifics of Lenovo's P52 or P53.

However, do note that the default upstream Xorg DDX (graphics driver; not to be confused with kernel video drivers) is provided by the server package (and utilized by Wayland I think), not a separate package. It's a single DDX that works for virtually all AMD, ATI, Intel and NVidia GPUs & APUs made in the past decade or more. GPU-specific DDXs in most cases when installed override utilization of this newer technology default. In fact, there has been no official release of the Intel DDX in over 4 years. Intel's driver writers' focus is on the default, named modesetting, not to be confused with modesetting as a component of the kernel's video drivers (KMS, chip specific, i915 for Intel, nouveau for NVidia, amdgpu or ati for AMD/ATI).

This "universal" modesetting DDX should enable the behavior you seek. Whether it might or not you're probably only going to be able to find out by trying.

In addition, the NVidia CRTCs may be explicitly disabled via kernel cmdline option video=<output>:d if necessary.