HTTPS Everywhere helps to encrypt your browsing and communication by rewriting all http connections in the more secure HTTPS, if the site we are using is compatible.
Windscribe uses AES 256 with SHA-512 and 4096-bit RSA key plus a firewall that allows the IP will never be exposed, even in the case of loss of connection with Windscribe.
So I think that HTTPS Everywhere is redundant when you are using WS.