On power up the ESC key will get you into the opening screen which is labelled 'Front Page' and offers you four self-evident options:
Continue
→Boot Manager
→Boot from File
→Setup Utility
On my system with a UEFI bootable USB drive plugged in the Boot Manager screen presented me with:
Boot Option Menu
EFI Boot Devices
[EFI HDD 1]: Windows Boot Manager (TS64GMSA370)
[EFI USB Key 1]: EFI USB Device (SanDisk)
[EFI Other 1]: Internal EFI Shell
Note: The system will only boot EFI devices. The Boot Manager does not recognise legacy boot devices.
Setup Utility takes you into the InsydeH20 Setup Utility and it's opening screen. The top line identifies it as InsydeH20 Setup Utility Rev. 5.0. In the Linux dmesg text I find:
efi: EFI v2.6 by INSYDE Corp. ..... SMBIOS 3.0.1 present. DMI: 10ZiG Technology 6000q-1/Type2 - Board Product Name, BIOS 6000q-1 V:3.C.216-09132021 09/13/2021 .....
...and it offers the following usual list of setup pages:
Main Advanced Security Power Boot Exit
The Security page tells me I have no TPM device present and is also the screen where you (re)set the supervisor password. (Default is 10ZIG). As noted above there is no option to select 'Legacy' booting, you're stuck with UEFI.
The Advanced page includes SCC Configuration which enables/disables the eMMC controller and SATA Drives which does a similar job for mSATA port.
→Boot Configuration →Video Configuration →SCC Configuration →HD-Audio Configuration →SATA Configuration
The Boot screen is where you enable/disable USB booting and set the boot device priority.
The BIOS doesn't include anything past the basics in what you can enable or disable: what you boot from, state of caps lock when you boot, wake up events, video memory size, eMMC controller enable/disable, SATA enable/disable, that's about it.
Having enabled the eMMC controller I noticed that the eMMC drive was recognised as 'bootable'. Having booted from it I found myself looking at a screen that identified itself as PXERecoveryLinux (Production) v5.20.048.1729. The opening menu was:
I have not explored this.