Thank you all !
Indeed setting execute perm on example, sub1, sub2, static
The program/user have now access to the directory.
In order words all the parents directory need at least execute in order to have access in the targeted directory...
Now I gave 751 for static. Meaning than others (here nginx) cannot list the files within. But never the less it worksthe static files are appearing when requested (HTTP) but forbidding nginx to list the directory is changing something ? (performance/security)
Thanks

Proxmox seem powerfull
It's a Type1, not Type2 https://en.wikipedia.org/wiki/Hypervisor#Classification