The purpose of that sqlite3 statement is to delete (“DROP”) that index from the database, if it exists. This error just confirms that it’s already gone. You’re fine to proceed with the remaining steps to attempt to recover your database. If it doesn’t succeed, you made a backup, right?
[Edit to add]
Also, several months back, UnRaid users were reporting persistent database corruption issues using Plex. I think this began after upgrading to 6.7.x. I don’t use it myself, but it was interesting to follow at the time. Here’s one of several threads discussing it:
