In Linux, the choice between MBR vs. GPT partitioning is completely independent of the choice between BIOS vs. UEFI boot method. With Linux, you can have a MBR-partitioned disk booted in UEFI style, or a GPT-partitioned disk booted in BIOS style - but since Windows does not like those configurations, dual-booting Windows in a system configured like that might be impossible or at least would require visiting the BIOS settings to toggle UEFI/BIOS boot modes every time switching between the OSs. The same might be true with other OSs whose boot configurations are not as flexible as Linux's.
You could always tell the installer to skip installing a bootloader, then after the installation is complete (but obviously not rebooted yet), switch to a virtual console that gives you a root prompt. Then chroot into the new installation, and manually install the BIOS version of the bootloader (i.e.
apt install grub-pc). It will conflict with
grub-efi-amd64 if it's installed, so you'd want to remove that first if necessary.
You'll then want to create a
/boot/grub/device.map file that says the USB-connected disk will be
(hd0) for GRUB at boot time, and then run
grub-install --target=i386-pc /dev/<USB-connected disk>.
While doing the installation on a UEFI system, the
grub-mkconfig (called by
update-grub) might add an UEFI-specific boot entry for booting into UEFI firmware settings, and that might cause an error if selected on a BIOS-based system. To get rid of it, just run
update-grub once the installation is running on the actual target system.