RedFox wrote:
most resources, be it on this wiki or in general, seem to refer to the legacy BIOS protocol.
Outside of bootloaders, you don't need to interact with the firmware at all, so for the most part you can pretend "BIOS" is equivalent to "UEFI" and ignore both. Unfortunately, some bootloaders seem to think VGA is a good idea, so you might have to specifically ask for a linear framebuffer to completely get away from the firmware. Of course, you're not writing a bootloader, so you don't have to worry about firmware. Right?
RedFox wrote:
There are a lot of tutorials and research papers writing bootloaders, kernels and all that stuff for older systems using BIOS instead of UEFI and the 32-bit x86 architecture instead of the 64-bit x86_64 architecture.
Beware: most tutorials are garbage.
As I already mentioned, the differences between BIOS and UEFI are mostly irrelevant. The differences between 32-bit and 64-bit are more substantial, but they're still the same CPU, so you can at least learn the basic concepts from any 32-bit-specific resource and then use the CPU manuals (and ABI manuals!) to learn how 64-bit is different.