Actually, it's not after install cause the errors shown indicate the initial admin user has not been setup - so install has not been finished.
Have any sort of web application firewall (WAF) - like mod_security running? Those 404's are really trying to pull in code from outside your nginx site.
Got ssh into your OVH server? If so, there is in moodlecode/admin/cli/ an install.php script that will prompt for the very same things web based does ... including the initial setup of the admin user - without interference from OVH protections.
'SoS', Ken