A custom URL for a google site
Go to Domains.
Click Manage domains.
Next to Primary domain, click Set up redirect or Change redirect.If your domain is managed through Google Domains, you may not see the see the redirect option. Click View Details, then Manage domain to set up the redirect in Google Domains. For details see Subdomain forwarding.
Enter the prefix or subdomain of the web address (typically, this is "www")Save.Note: Address mapping is supported only by HTTP and not HTTPS.
Configure A records for your domain to map the prefix you entered above to the IP addresses of Google servers hosting your site.You configure A records using the administrative tools at your domain host, not the Google Admin console. If you don't know how to configure A records, see A record values.
When you're done, click I've completed these steps.
You might have to wait up to 48 hours for your A record changes to go into effect. After that, entering your naked domain address redirect to the web address you set up in your Admin console.