I'm somewhat hesitant to call this a bug, because maybe it's not supported, but I installed violentmonkey Chrome extension, and I have a simple extension that basically checks title tag of Gmail page and sets a badge counter if there are any unread emails. This works well in Vivaldi for using Gmail as a standalone app. I wanted to do the same with Orion, but this doesn't seem supported:
TypeError: navigator.setAppBadge is not a function. (In 'navigator.setAppBadge(m[1] | 0 || null)', 'navigator.setAppBadge' is undefined)
Supposedly webkit supports this: https://webkit.org/blog/14112/badging-for-home-screen-web-apps/
Thanks.
Ideally, the setAppBadge API is supported for web pages installed as "apps", similar to how it works in Chrome.
Version 0.99.126.4.1-beta (WebKit 618.1.2)
Sonoma (14)