PS5 hotfix 1.14.105 has released and appears to fix the Chaos Rune bug

Currently unsure if any other platforms have gotten updates that fix the bug yet.

1.14.105 was already the current version for PC when the bug was found, and Poncle haven't posted an updated patch notes with PS5 getting it (I wouldn't be surprised if they simply don't publically acknowledge the weapon existing at all for a while longer, though).

It's likely the PS5 1.14.105 is a slightly different build; if your game's updated today check if this fix has made it to your platform as well. It's likely the next hotfix for each platform is going to fix this bug.

...the weapon's a lot better than I expected, as well.