Roughly how many certificates did you have for the deleted domain, and how often is “
certbot renew” configured to run?
If you had 1 certificate and run it once a day, it should only create 2 files per day, or 730 per year.
If you had, say, 15 certificates, and run it every 6 hours, it could create almost 45,000 files per year…
Edit: That still doesn’t approach your situation of more than 200,000 files, though.