An Azure search service with built-in artificial intelligence capabilities that enrich information to help identify and explore relevant content at scale.
Thanks for posting this question.
To better assist you on this - is this issue confined to any specific PPTX file or all PPTX files? Does the other document format index fine?
From the same docs that you referenced – yes, PPTX is supported document format.
Also, please check the Limitations and considerations - Index data from SharePoint document libraries.
To begin with, On Azure Portal, on the Search Service, in the left navigation, click on Diagnose and solve problems – Checkout the tile highlighted files/troubleshooter recommendations (if you haven't done this already).
To isolate the issue, kindly check if there are any error messages
-cognitive-search-common-errors-warnings - This article provides information and solutions to common errors and warnings you might encounter during indexing and AI enrichment in Azure AI Search.
- search-indexer-troubleshooting#missing-documents -This article covers problems and potential resolutions when indexer results are unexpected and there is limited information to go on.
Kindly let us know, I’ll follow-up with you further.