"Fast boot" support is likely enabled by default, and skips showing you the OS list.
Hold Shift when clicking "Restart" from within Windows 8, to get the Windows Boot Manager to show up - it should let you get into the UEFI settings screen, as a bare minimum.
Re: Fedora 28 does not work with Sony VAIO
Hold Shift when clicking "Restart" from within Windows 8, to get the Windows Boot Manager to show up - it should let you get into the UEFI settings screen, as a bare minimum.