For the most part, it seems a large majority are fine. But it's expected to find these issues on a new platform/launch. It's just refreshing to see AMD already found a large fix for Linux users.
Going off the information we have, I would guess it's not the bios specifically, but the Ageasa(however it's spelled) that contains the firmware fix that would fix Destiny 2's issues. It's just packaged with the BIOS. It would be due to the specific functions the Destiny 2 codebase is using that the CPU is processing weird. Could be it's expecting something completely different and or runs a certain way the Game Engine isn't expecting.
I am probably wrong but it's not surprising I guess. Zen 2 is kinda different than Zen 1 so their optimizations for Zen 1 aren't running right on Zen 2.