@TSUSOLS
As @Fernando suggested, let’s assume that your motherboard is the Gigabyte GA-870A-UD3. It looks like it was designed back in ~2010-2011. As said, this is a non-UEFI motherboard.
A solution to install an OS on an NVMe SSD in your system is to use an NVMe PCIe adaptor, and then to use the Clover bootloader.
In fact, this is what I did on an even older motherboard, and it works fine. See my post here.
Let us know if you wish to proceed further in the Clover path. I will be glad to provide further assistance.