I've updated bioses both from a bootable and non bootable USB stick, the latter being triggered either from Windows or UEFI, and also used the motherboard update program in Windows, some of which download a new bios. And used a dedicated bios update program either in Windows or in UEFI, again either self downloading or requiring the new bios been downloaded and unzipped. Lots of variables there.
Not too long ago there was a motherboard that despite finding a new bios through the UEFI update program could not install it, neither did it accept the latest bios when downloaded through Windows. But I managed to get it a couple of versions forward with the latter method. Can't remember the brand, might have been AsRock.
Anyhow, usually any of the methods provided by the manufacturer work. The Windows version is the least effort way.