Just found my Vivaldi update contained a little more than just bugfixes… it now has Proton VPN built in.
It’s actually part of the browser, not an extension, so I’m in two minds whether I like that… or not.
You need either a Vivaldi account or a Proton account, so it’s not completely anonymous, but it’s a start.
The free-tier of Proton VPN also appears to be bandwidth limited and your exit point is randomised, so… yeah, it’s ok…
It’s not turned ON by default. It’s just there as an option, you are opting in to use it if you want to use it.