Additional Config
We strongly advise against including any config not configurable via the UI as it will most likely interfere with settings automatically computed by the updater. Additional configuration options are not supported so we encourage you to first raise your requirements to Support where we can best advise on them.
The Additional Config section, which allows including config not currently configurable via the UI from the Configuration Manual, is available under the 'Advanced' section of the Synapse page.
Configuration should follow the same format as supplied by the Configuration Manual, if you include options that have otherwise been configured via the UI they will be overridden with the exception of MAU, Federation and Data Retention. Though as noted above, this will most likely interfere with settings automatically computed by the updater.