I carried out a quick test of the InsightIDR plugin which was updated to v4.0.0 at the end of last month to include Investigation-related actions like Search Investigations. I wanted to see if it would return Investigation ID, but it doesn’t since the plugin is a wrapper for the InsightIDR v2 API.
Please know that I truly appreciate the replies I get here in the forums, as well as the significant dev work which goes into all of these plugin enhancements. In this particular case, thank you @david_smith and @igorski, as well as many others who have spent time developing and/or helping me with the components I’m asking about.