Forward Naked Domain

If your domain provider lets you redirect your naked domain to the subdomain address (e.g. make example.com redirect to www.example.com) then configure that

Alternatively add an A record of @ (or your naked domain) that points to 174.129.25.170 (a free service from wwwizer.com)

From https://www.steegle.com/google-sites/how-to/assign-custom-url-domain-personal

Forward Naked Domain - GoDaddy

Google Domains - Use a Synthetic Record

See Steegle's Instructions