The integration lives on the Splunk side, not the Nextcloud side — there is no Nextcloud app for Splunk. What you are looking for is a Splunk add-on that ingests Nextcloud logs.
This came up here before: Splunk App for Nextcloud — the links in that thread are dead now, but the add-on still exists on Splunkbase as an unsupported community app:
Since it is a Splunk-side add-on, questions about setup, compatibility, and missing features belong on Splunkbase or in Splunk’s community forums rather than here.
I originally created the Splunk add-on and app as a personal project while I was working at Splunk.
From what I understand, the current version no longer works properly with newer versions of Nextcloud, although I would need to spend some time investigating whether that is due to log format changes, parsing changes, configuration differences, or something else.
I would still like to revisit it at some point, but realistically it is not something I can prioritise in the short term alongside other commitments.
That said, if there is enough interest from people who would be willing to help test, provide sample logs, or sponsor the update effort, I would be open to discussing what it would take to bring the add-on and app up to date.