OK, I set up a brand new site under a different site name. Went through the initial setup to add the admin user.
Then I restored as instructed.
404 not found message when I visited the new site!
Then I tried a bench migrate, in case that was the problem.
Still 404 not found.
This is a 404 message generated by frappe, not by my host nginx proxy. I can see the various GET requests in the logs.
"GET / HTTP/1.0" 404 120697 "https://crm.test.example.uk/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36"
"GET /assets/frappe/images/ui-states/404.png HTTP/1.0" 200 96089 "https://crm.test.example.uk/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36"
"GET /website_script.js HTTP/1.0" 200 25 "https://crm.test.example.uk/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36"
"POST / HTTP/1.0" 200 13 "https://crm.test.example.uk/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36"
"GET /assets/erpnext/images/erpnext-favicon.svg HTTP/1.0" 200 455 "https://crm.test.example.uk/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36"