> And at least according to this, the default setting is off

It appears to not default to off on my install (AlmaLinux 10).

I just tested now. Cloudflare normalises ../ and ./ paths and then the nginx proxy appears to normalise // to /:

nginx log:

  1234:: - - [18/Apr/2026:12:59:05 +0000] "GET //test//doubleslash/url HTTP/1.1" 404 158 "-" "curl/8.19.0" "1234::"

  1234:: - - [18/Apr/2026:12:59:04 +0000] "GET /test/doubleslash/url HTTP/1.0" 404 158 "-" "curl/8.19.0"

Actually I think you’re right, here it also says the default is on:

https://nginx.org/en/docs/http/ngx_http_core_module.html#mer...

Thanks for trying!