I was already using Cloudflare DNS using their nameservers at Google Domains. Now, I have switched completely to Cloudflare registrar.
The process of domain transfer is so simple. Just keep domain unlock and provide auth code to Cloudflare.
There is no way to set third-party authoritative DNS nameservers.
User on Business plan can set vanity nameservers.
I transferred two domains so far. It took less than 10 minutes. Looking forward to do more.
Official Blog post
Get started https://www.cloudflare.com/products/registrar/
Thanks & Regards,