"...seems that filtering in not supported on Universal Forwarder"
It's only supported for Windows EventLogs as described in the input.conf documentation:
Filtering in input.conf on the indexer wouldn't make any sense. You could only filter the Windows EventLogs on the indexer. It works for UF.
# Windows Event Log Monitor
blacklist = << list >>
Tells Splunk which event IDs and/or event ID ranges that incoming events must NOT have
in order to be indexed.
Optional. This parameter can be left empty.
A comma separated list of event ID and event ID ranges to exclude (example: 4,5,7,100-200).
If no value is present, then there is no effect.
If you specify both the "whitelist" and "blacklist" attributes, the input ignores the
"blacklist" attribute.
whitelist = << list >>
Tells Splunk which event IDs and/or event ID ranges that incoming events must have
in order to be indexed.
Optional. This parameter can be left empty.
A comma-separated list of event ID and event ID ranges to include (example: 4,5,7,100-200).
If no value is present, defaults to include all event IDs.
If you specify both the "whitelist" and "blacklist" attributes, the input ignores the
"blacklist" attribute.
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