Any ideas on how I fix this and get my IVACY subscription running on LibreELEC?
LE10/LE11 images use Python 3.x, the last release to use Python 2.x was LE9.2. So options are:
a) Persuade <insert name of whatever VPN service> to provide a Python3 compatible version of their add-on
b) Find and extract the connection details and credentials/certs used from the add-on and use them with e.g. Zomboided's add-on.
Option A has no further action from us (the add-on, the service, and everything related to it is someone else's problem). If you go for Option B redirect future Q's to Zomboided's add-on support thread.