In the old post from when the update was released a Heise article is linked, that contains indicators of compromise, and in turn links to Kevin Beaumont for the details of his analysis:

https://lemmy.zip/post/54712916
https://www.heise.de/en/news/Notepad-updater-installed-malware-11109726.html
https://doublepulsar.com/small-numbers-of-notepad-users-reporting-security-woes-371d7a3fd2d9