The only way of tuning early_hint_header_mode is via global settings.
This is generally done by setting environment for the container:
DISCOURSE_EARLY_HINT_MODE can be preconnect or preload or prefetch or blank.
Self hosters would do so in that app.yml file.
This setting is only able to come with one value. Self hosters can validate what it is with:
./launcher enter app
rails c
> GlobalSetting.early_hint_header_mode
Early hints are a rather complex setup cause the proxy needs to support them and they are not supported by many proxies.