There’s a known memory leak. Blizzard hasn’t really responded with anything aside from “we’re looking into it”.
D4 has run out of RAM? - Technical Support - Diablo IV Forums (blizzard.com)
Beta has a massive memory leak issue, using over 20GB of ram. : diablo4 (reddit.com)
So yeah if you’re having entire system lock ups and need to force restart your pc, I would guess that this is the issue. However, a memory leak shouldn’t “fry” a graphics card. It just causes a system error, and a force restart should be fine.