Short the DNS standard is old and from a time where every website was hosted on www.domain.tld it only supports CNAME for subdomains.You can use cloudflare as your DNS provider and use your current settings and it will work, they emulate it with continuously updated A and AAAA records.There are other DNS providers that also do the same thing I'm not sure which ones as I use cloudflare.On other DNS providers if they support this behavior they have a separate record type called ANAME or ALIAS so look for that when you choose a provider or try if ANAME/ ALIAS work at your current provider.Edit: railway has docs for this showing you some providers that work and how to change your nameservers to another provider if your current one doesn't support it https://docs.railway.com/networking/domains#adding-a-root-domain