Yes, when I try to proceed with adding the custom domain, at the second step after entering the domain name, it takes me to Transfer DNS management page:
I found the issue: When I first started the project, I began on a different account and added the Apex domain to that account, but I didn’t continue from there. I didn’t add the NS records provided in that account, so it remained pending (and I forgot about it until now). In short, the domain was not active in that account.
As soon as I removed the domain from the first account, I was able to associate it as a custom domain for the deployments in the primary account.
This might cause an issue/bug since someone can add a domain to their account without verifying the ownership, and the owner will not be able to use their domain in the Cloudflare products.