It feels like a million years since SLI was relevant, and even during its heyday, the prospect of running multiple graphics cards to boost performance in games had some serious downsides. Like cost, stuttering, and the fact that performance was not consistent across all games. None of it matters now, because SLI has been put on life support. Starting January 1, 2020, Nvidia will stop adding new SLI profiles to its GeForce driver packages.
Technically, SLI is not dead, but if this was an episode of The Walking Dead, it would be the one where it gets bit by a silicon-eating GPU. SLI is going to live on for a bit, supposing game developers decide to put the work in supporting the technology themselves without the benefit of specific SLI profiles at the driver level. But its days are numbered.