When you die outside the border, it would be great to have a way to handle that, whether that's moving the grave inside the border or to a chosen location. I have a mod that changes where the border is quite often, and it can cause some distress :P. I remember this worked in an old 1.19 version, perhaps it's something to do with the "placement" configuration?

So things work right if worldborder is static, but break once it moves (or rather, graves are static so they can leave outside of wb). I can look for a clean solution, but won't promise anything.