I've used Core Data for over a decade, all of my Core Data apps have used SQLite in the background. I've also tried some apps with SQLite.swift and GRDB.swift. Core Data is based on SQLite and should be able to handle large databases, but in my experience really slows down when you have a table with more than 10,000 rows. Not sure why. Also I'm not happy with the SQLite database underneath Core Data being off-limits. I can understand Apple's reasons. They want everything driven by their GUI leaving them free to optimize behind the scenes, but I'm trying to work on a synchronization with outside data. SQLite.swift and GRDB.swift work, but not as cleanly as I'd like. However I haven't seen the slowdowns with my 80,000 row table that I've seen with Core Data. I just started experimenting with MongoDB Realm. It's cloud sync looks more robust than Apple's Core Data / CloudKit sync, but I haven't hand enough time with it to be sure. One worrying sign to me about Core Data. Past WWDC's have had many Core Data sessions. This year I only see two on the schedule. I was hoping for a more Swift-friendly update to Core Data this year. Doesn't look like it. Unrelated to your question, but on a similar note, I don't see any Combine sessions on this year's schedule.

As the previous comment says, You will have to restore the data from a backup after you re-install iOS 13. However, backups made during iOS14 might not be able to be restored under iOS13. In previous iOS releases backups made under new versions could not be restored under a previous version.

"presumably you can configure your model's id field to be indexed, allowing for efficient lookup." I do have the id indexed, but now I have to search on up to 12 tables when I only have recordID and not recordType.