When you connect to a secure (https) website, Vivaldi and other browsers use various protocols to establish a secure connection with the website. All data is encrypted so that only the browser and the website can see what is being sent over the connection. Anyone else who can monitor what is being sent over the network would be unable to decrypt the data, at least not within a reasonable timespan.
That is misleading. If a site uses https, that only does make the data encrypted after the handshake, and the hostname of the site is being sent cleartext during DNS lookup and initial connection. So anyone who can monitor the network still sees what sites a user visits. You even have this info in the article about VPNs.
Please add this info in the paragraph about https with the link to the VPN article, so that readers unfamiliar with this do not think that https fully secures privacy.