MySQL Plugin failed to install due to "undefined symbol"
It's not really an answer, but I found a workaround, which is to use the Percona Audit Plugin instead (which I used to use anyway, but stopped working when I moved from 5.5 to to 5.7, but strangely now works again with 8.0). In my case I already have the support code and infrastructure to switch back to this so it's not a big task.