Forward blog.xx.com or directly *.xx.com to your server from your domain name manager

Then configure nginx or Apache. You can search for the specific operations. It’s hard to explain clearly here because I don’t know your various configurations.

Just go to the domain name registrar to apply for the top-level domain name xxx.com, such as Wanwang, Godaddy and other service providers.

Then log in to the backend and you can configure the second-level/N-level domain name at will:

blog.xxx.com
wx.blog.xxx.com

Friendly reminder, if it is a domestic domain name registrar and is hosted on a domestic server, it needs to be registered.

Register or purchase xxx.com

Then set the A record of the blog.xxx.com subdomain name in the domain name DNS console by yourself

Domain name resolution, A record
General websites will set up a www.xxx.com
You can set up a blog.xxx.com