Question PH315-53 How to set Boot Drive Password

[Acer laptop]

Hello, I am trying to set a password on the boot drive. BIOS will only give me the option to set a password on the second HDD. Searching the web one forum suggested it is not possible to set a password on the boot drive. It is possible on other laptops, it should be possible on this one. Does anyone know how to set a password for the boot drive. It is an m.2, but that shouldn't matter should it? Following the FAQ at the Acer community to set a password on the hard drive only works for the second drive i have installed, not the primary, boot drive.