You could try to delete EFI files from USB flash
(if you delete EFI files,The USB flash only support bios and mbr. )
I writing to USB flash(Sandisk USB 3.0) by Rufus(Windows 10),and boot from USB flash,I see a boot menu for UEFI. I do not know why the system into UEFI mode. The computer doesn’t support UEFI and GPT. I want to install system in Bios mode.I don’t know how to solve it. I hope to get help.Thank you.
###Here is specific information I installed System
Computer:Lenovo Z475, A6-3400,Bios Motherboard,6GB ram, usb2.0
Installation Tools:Rufus,Win32DiskImager, dd.exe,Universal-USB-Installer-18.104.22.168,UNetbootin (i try to use different tool to writing to USB flash)
ISO file: manjaro-kde-16.08-x86_64.iso
USB flash: SanDisk Ultra USB 3.0