Bios shows Android and Windows 8.1 in Windows 10 PC

Solution 1:

This upvoted comment seems to be a tentative answer or clarification about the situation in question:

Looks like you are talking about an notebook with ARM CPU if Android is installed by default and selectable in BIOS. What you want to use is your choice. (...)

I disagree with the above statement on both counts:

1. It shows an "UEFI" settings interface typical of a x86_64 hardware architecture, not ARM and
2. that selection/option doesn't mean "Android is installed by default", it doesn't mean it is installed at all, let alone "selectable"

What you're seeing is actually an arguably "weird" UEFI implementation where "OS IMAGE ID" is intended as the Secure Boot toggle:

• "Windows 8.1" => Secure Boot ON -> Should be selected for any Windows 8.x or newer with Secure Boot (it can be used for dual-booting with or standalone desktop Linux if you don't mind using mokutil to define trust but generally not recommended)
• "Android" => Secure Boot OFF -> Should be selected for any circumstance other than the above, i.e., if dual-booting with or standalone desktop Linux distro (without Secure Boot) and/or "Android for x86" or derivatives (mandatory).

In many computers with similar APTIO firmware with said toggle switch selecting "Android" instead of the default is strongly recommended because even if users don't mind the Secure Boot nuisance, the "Windows" option often results in (Linux) not being able to shutdown properly, hanging/freezing in the slash screen.

Other UEFI implementations may show "OS selection" (same thing, slightly different name) and other options like "Linux", "Windows 7" (typical in early implementations) or "Other". They all do the same, toggle Secure Boot ON or OFF.

That's all. Weird indeed but not such a mystery once we understand the above and certainly doesn't mean it came with Android preinstalled.