We are currently running the "Server" version of Confluence in our environment. This version doesn't actually store audit logs locally to a directory. Instead, the logs are only visible through the UI and can be exported from there with a max of 100k results. In that case, how would one be able to get these audit logs sent to Splunk in a programmatic manner rather than manually downloading the logs and uploading to Splunk on a periodic basis.
Here is a page which talks about Confluence audit logging and how it is lacking in capability for the "Server" version. The "Data Center" version, which we don't have, logs locally and can easily be sent over to Splunk via UF.
https://confluence.atlassian.com/doc/auditing-in-confluence-829076528.html
Have you tried using confluence REST API? You can try splunk modular input to call confluence rest api to import the audit data.
Below are some documentation references for both confluence & splunk that will give some direction
https://confluence.atlassian.com/cloud/audit-logging-970612562.html
https://docs.splunk.com/Documentation/SplunkCloud/8.0.2004/AdvancedDev/ModInputsIntro
Hope this helps.