WiFi issue brand new 16" MBP - self-assigned IP address
I see two possible problems here:

First possibility is that your MAC address after reboot is somehow invalid (i.e. for example set to all zeros). That could make your DHCP server (probably in your home router) reject your request for an IP address).

Check if that is the case by running the following command in the Terminal:

ifconfig en0


Note the line that starts with "ether" - it should have a valid MAC address looking something like f2:23:48:a3:1e:22 or similar.

Second possibility is that the problem is really with your WIFi router / DHCP server and not locally with your laptop. This could happen if your router added the new MacBook Pro's MAC address to a block list or similar.

Check the router's settings and management interface to ensure that the MAC address of your new MacBook Pro is not listed in any black lists - and if you have white listed your old computer, then white list your new computer as well.