Is there a shrink database/shrink file running? Does the DB have autoshrink enabled? Is there another index operation running on that index?

There's a lot of things wrong with that, but the most obvious is that the FROM is not followed by a table or subquery. Looks like there's a SELECT missing.

Keep in mind that Developer edition is not licensed for production usage. So by using it in prod, you're at risk of audits hitting you with a lot of fines.

You can't. You'll have to rewrite it as an SSIS package.

My plans for the year include the rest of the Expanse series, to try and make a dent in the unread Data and Machine Learning books I've bought, to read...

If there aren't too many foreign keys and the amount you're deleting is more than the amount of rows you want to keep, it may well be faster to insert...