I was able to track down the files in question, in case anyone else in the future needs to know. For StoreKit testing on Mac catalyst, check the directory: ~/Library/Caches/com.apple.appstoreagent/Octane The sqlite file store.db contains a table octane_transaction with the transactions in question, and I was able to delete my 23,000 test transactions from it.

It is a Mac Catalyst app. The app runs on macOS 12, it does not require an M1.

Submitted as FB9790739. Thank you!

Of course you can delete transactions with the UI, perhaps many at a time, but I had 23,000 transactions to remove and the UI couldn't handle deleting them in that kind of bulk. It would lock up/crash. The only way to restore it to its virgin state was to just trash the store.db file.