That would be a System Reserved partition. Recommended partitioning details are provided in two Microsoft TechNet articles for BIOS/MFT boot drives
and UEFI/GPT boot drives
In either case, the system needs to find the boot manager (either bootmgr or bootmgr.efi) and its boot configuration data (BCD) store in order to display any boot menu options for selection.
Your system UEFI configuration is responsible for telling it where to look, in what order, and if compatible with both types of booting, which one has priority. In some cases, it may also have
a setting to enable/disable the so-called "safe boot" feature. Windows 10 also has its own "fast startup" feature (actually it uses a type of "hibernation") that can occasionally be problematic
when system set-ups are changed, especially for laptops. This TenForums article
explains how to turn it off and on again which may be worth trying.
There's no harm in trying the "Fix Windows Boot Problems" utility option that is available in the Reflect WinPE rescue environment as explained in this KB article
. It's basically the equivalent
of Windows own repair tools. If you decide to do that, just be sure to follow the instructions for the type of booting (BIOS/MBR or UEFI/GPT) that is used by the computer being repaired.
Regards, Richard V. ("Arvy")