If you find the font rendering in Vivaldi looks out-of-focus, here’s the fix. Go to vivaldi://flags (that’s a URL!) and find:
“Disable DirectWrite Windows”
Then you enable it. Yes, you have to enable disabling it. When you restart Vivaldi, your fonts should render as crisp as a new fiver.
Tip found here: https://vivaldi.net/forum/vivaldi-browser/2237-font-rendering-in-vivaldi-is-an-issue