The old macOS 10.15 machine I was using for testing Vivaldi has been upgraded, despite not supporting newer macOS versions.
It actually can run @Vivaldi 7.0 despite reports to the contrary you might have heard.
https://vivaldi.com/os-support-notice-10-15/
ℹ️ I went with the third option (🐧) under "What can you do now?" in the above article. 😉
It has many more years running @Vivaldi and getting OS security updates left in it.
P.S. The built in camera and mic worked out of the box and the Apple mouse was simple to add. Just added as a new bluetooth device. All in all, no real issues to speak of.