How do I know what graphics cards are compatible with my computer
Someone asked a very similar question a couple of days ago. I'll write what I wrote on that thread as a post here:
Laptop graphic cards are not replaceable, not conventionally anyway. Where would you even buy those? Laptop graphics cards are not sold by themselves. You can only find them in expensive bare bone build-your-own laptop kits.
And to add even more stress, you'd have to disassemble your entire laptop first. I've disassembled laptops before, but it's an extreme hassle. If you have little to no experience, then there's a chance you could wreck your laptop completely.
And even worse, the GPUs inside a laptop are also soldered right onto the motherboard, so replacing them is more than just a hassle. It's almost impossible unless you have proper equipment, and I'm not even sure how they interface with your motherboard. I don't believe it's PCIe, not unless they're specialized laptops and I have no idea if there's even a standardized method to connect any non-PCIe GPUs. The BIOS probably wouldn't even recognize a new card for a number of reasons. Only the most expensive laptops allow for a replaceable GPU.
And yet again, there's another problem. SLI means that there's 2 (or more) GPUs. SLI is a term coined by and applied by Nvidia to describe a technology in which 2 GPUs work in unison with one another to theoretically double the power. That means that even if you somehow solved all the problems up to this point, the problem you'd certainly run into is that your laptop motherboard would need an additional slot in which you could place the second GPU, and unless you have access to expensive modification equipment and a good knowledge of computer engineering, that's damn near impossible without replacing the motherboard all together (which would be even more of a hassle).
So in short, it's just about impossible unfortunately. It might be a good project, and I'd totally try it on my own if it weren't so damned expensive to do so. If you have plenty of funds to throw at whatever you want (and we're talking a lot of money here), then you might go for it just because it could be fun but if you're like most of us then unfortunately it's just not a feasible thing.
To summarize, and to contextualize it a bit to make this more relevant to your post, only graphics cards designed exclusively for laptops (they'll be designated usually by an "M" at the end of their name) are useable in laptops, and the problem is that they're rarely sold by themselves and they can't be easily replaced unless you have a higher end laptop made specifically to be able to switch out parts like a graphics card. Any other laptops have the graphics card soldered right onto the motherboard, so you'd have to have soldering equipment to replace it and there's no guarantee that your motherboard would even recognize it if you did.