Finally. Most important features that kept me from switching to chrome, brave or any other browser was: 1. The sidebar with tabs that shares the same state over multiple windows. 2. The preview windows that open directly where you open a link.

The dual engine approach is interesting, never seen that

Appears to use Chromium by default, and also ship WebKit to toggle for individual websites: https://crestbrowser.com/guides/engines/

Of course this comment section also warrants a mention of Zen Browser, another Arc alternative that's been going for a while already, is based on Firefox, and is available cross-platform: https://zen-browser.app