You can actually install install UEFI boot manager on a legacy bios.
You can use
for example, this will allow you to boot EFI sources. The way it works you will need a usb pendrive which has a legacy bootable partition (with Tianocore installed and configured) that will boot your EFI partition (Windows for example). You will have to keep the pendrive plugged in so that you can boot the EFI gpt partitions or bootloaders.
I have done this on couple of old legacy HP machines to get PCIe NVME working as a bootable drive.