Settings - Server - General - ‘Show Advanced’ - “The path where local application data is stored”
put D:\ into there, instead of just D:
Afterwards you can update again.
If you haven’t downgraded yet, shut down Plex and edit the registry instead.
https://support.plex.tv/articles/201105343-advanced-hidden-server-settings/
The key LocalAppDataPath is the one to edit and add the backslash \ to
