Hi @evodreamfr. The * CNAME record should cover all subdomains when you’re using Vercel nameservers. Try removing the test CNAME and let me know if that gets it working for you.
The 404 is a bit trickier since there are a lot of different reasons that a file may be at a different location or missing from a deployment entirely. This post has tips to help you locate the source of the problem: Debugging 404 Errors