There's another community post with 404 debugging tips that might be helpful. Please give these solutions a try and let us know how it goes.

https://community.vercel.com/t/debugging-404-errors/437

Vercel Community

Debugging 404 Errors

Sometimes things don’t go as expected when deploying a website. If you see a 404 on your site, that means the page or resource couldn’t be found. There are...

A human should be around soon to offer more advice. But you can also get helpful information quickly by asking v0.

Looks like there's nothing deployed at the URL you shared. I'm guessing that was one of the deployment domains for the old project you deleted.

Please check that you have the right domain and make sure there were no build or deployment errors. The 404 debugging guide has tips that help with most 404 errors we see here. Give those ideas a try and let me know if you still need help after that