In the process of moving over from Opera, so far I've adjusted well but there's two key features I miss.
What I miss the most, a massive creature comfort for someone who does alot of reading,
Clicking the active tab to scroll to the top, and being able to click it again to return to where I was.
The home button emulates it to an extent, but being able to do that & return in 1 click, I miss that.
Otherwise, selecting text in Opera GX has a popup context menu, it allows you to copy, search, goto, etc. without right clicking, just a changeable delay before it pops up above your selection.
That functionality is available in Swift Selection Search I've linked below, but one big thing its missing is:
If you select something like "$45", it'll take in context and popup your local currency equivalent, select something like 4x20 and it'll popup "=80" and you could hover over the popup and it would change to "Copy",
maybe "4:30 (GMT-6)" to local time, temperature conversions, etc.
Small things overall, but the utility of these had me itching to go back before I found Swift Selection Search
Editing this in a little afterwards: In Opera if you have two duplicate tabs open and you hover over one of them, the other gets highlighted in the tab bar, this is massive for clarity when crawling through stacks of tabs.