Sourcetypes are tied to data collection.
1- If it is mod input (built in Addon builder) it automatically shows on the list
2- If it is data indexed by Splunk core such HEC or syslog, you will need to import it by clicking on "import from splunk" button under "add sample data tab". Once you have imported it, it becomes visible to you in Addon builder so that you can apply knowledge ( field extraction and cim mapping) as part of the add-on
3- if you want to add file monitoring in addon, click on "upload from file", it becomes visible to you in Addon builder so that you can apply knowledge ( field extraction and cim mapping) as part of the add-on
This has become a common question we get, we will improve the UX to make it more clear in furture but hope this answers your question.
... View more