My DNS provider limits record length. Can you shorten the DKIM key?

No. The DKIM key length cannot be reduced, because it is a security measure. If your DNS provider cannot hold the full record (some limit records to about 250 characters), use a DNS provider that supports it, such as Cloudflare.

You do not have to move your domain registrar. Keep the domain where it is and point its DNS to Cloudflare, which supports the full record. Our support team can help you with that if you need it.