I can't install plugins on OctoPrint?
This is a known issue (WIFI fine, but no internet connection to install plugins) and could well be related to firewall or blocking of certain ports by your Internet Service Provider (ISP).

I quote from the provided link (OctoPrint issue tracker):


  Disabling the connectivity check did fix the repository access. The check was configure to use google (8.8.8.8) on port various ports (22, 53, 5000, etc. Not sure the default). I do not have any firewall set up outgoing, unless it is buried in the Raspberian install that I am not aware of.





  I stumbled across this issue with the same problem, and I fixed the connectivity check by changing the IP to OpenDNS with 1.1.1.1 instead of the Google DNS 8.8.8.8 set by default.





  For me this issue was resolved when I update Date+Time on the raspberry...