Uploading larger files like 7GB, ERROR: Could not open file

[jtr]

@xGuys

fastcgi_read_timeout 4800;

This is the likely relevant value (e.g. see here).

And AFAIK it needs an s appended to it as described in the Nginx docs: Module ngx_http_fastcgi_module

Some of your other values may be impacted by that as well.