https://libreboot.org/docs/install/#which-systems-are-supported-by-libreboot

Sí.

It depends on the specific chipset of the motherboard.

Frankly, you shouldn't attempt to replace BIOS/UEFI until you understand what it does and why it's such a complicated problem to solve.

There's a specification document: https://uefi.org/specs/UEFI/2.11/

You don't need to understand the whole thing (I doubt any single person alive understands all of it), but you should read the Introduction chapter, especially the Organization, Goals, and UEFI Design Overview sections to get a handle on the broad concepts, and then skim some of the rest of it such as 2.1 Boot Manager and whichever hardware platform section is relevant for you under 2.3 Calling Conventions. This will help you understand some of the relevant terminology and details about how your hardware communicates which may be helpful for troubleshooting.

https://uefi.org/specifications

UEFI was first released in 2006, replacing BIOS which was implemented as a standard in 1981 but grew out of older projects. Understand that you're talking about replacing a complex system with 50+ years of development behind it, which has been rigorously tested, with a substitute that has a far shorter development lifespan and far less field testing.

It's great to want to try something like this as a learning experience. This layer of computing is often overlooked, though basically everything depends on it. It's worth exploring. But, you should assume that any system you do this with is unstable, and probably sacrificial.

tried flashing a Lenovo T480 with Libreboot, following the instructions on their official website

Maybe they made some improvements recently? I did this last summer.

oh lol i messed up, just edited..