Ensure the laptop is fully powered off.
Once the BIOS menu or Dynabook logo appears, release the key. toshiba dynabook bios boot
If you only need to boot from a USB drive once (e.g., to install an OS) without permanently changing settings, use the : Follow the full shutdown steps above. Insert your bootable device (USB, DVD, etc.). Power the laptop on and immediately tap F12 repeatedly. Ensure the laptop is fully powered off
If you need to change settings permanently (e.g., switching from UEFI to CSM mode to support older operating systems), you need to enter the BIOS. you need to enter the BIOS.