Intel problem which they said they won’t be fixing, so it is up to Plex to work around.
Multiple was to suppress the iHD driver that survives upgrade have been provided, here is one.
You will need to change PMS_IP to the IP of your NAS, and change MY_TOKEN to your PMS token. (https://support.plex.tv/articles/204059436-finding-an-authentication-token-x-plex-token/ )
http://PMS_IP:32400/:/prefs/set?VaapiDriver=i965&X-Plex-Token=MY_TOKEN
(Just copy and paste that into your browser and press enter)