I ran into this issue 2 years ago when Cloudflare Registrar first launched… and it looks like it’s still an issue. The dreaded “DNSSEC is pending while we wait for the DS to be added to your registrar” message which never goes away. You can wait 200 hours, enable/disable DNSSEC a million times and your domain will still never have DNSSEC.
On the Cloudflare Registrar product page “one-click DNSSEC” is advertised as one of the many benefits, but I’ve clicked a dozen times now and waited many hours. DNSSEC is easier to implement when using an outside registrar.
This was acknowledged as a known issue back in Dec, 2018 here: Stuck Pending While Setting Up DNSSEC On Cloudflare Registrar