I too lost over 100 tabs I'd been using for online research when Opera 'upgraded' to Opera One, at one point they were all there, and I sorted them into the Tab Islands, then they were gone.

Also I appeared to, at least on the day of the 'upgrade,' have more than one version of Opera open, not sure how, but sometimes 'One' would appear, with all the tabs, other times another version of Opera would appear without any tabs.

For the moment, I've stopped using Opera and reinstalled Firefox, something I've not used since 2017.

I've no idea how I can get my missing tabs back, and as they weren't the most recent in my search history, it would probably be quicker to start afresh.

Meanwhile, I still have no idea how to reclaim the tabs OperaOne decided to lose after allowing me to sort them out into Tab Strips.

You know what I, and I suspect many other want in a browser? Stability, and not to lose our tabs/favourites after an 'upgrade' is forced upon us.

I've gone back to Firefox after some 7 years as an Opera user.

I too lost over 100 tabs I'd been using for online research when Opera 'upgraded' to Opera One, at one point they were all there, and I sorted them into the Tab Islands, then they were gone.

Also I appeared to, at least on the day of the 'upgrade,' have more than one version of Opera open, not sure how, but sometimes 'One' would appear, with all the tabs, other times another version of Opera would appear without any tabs.

For the moment, I've stopped using Opera and reinstalled Firefox, something I've not used since 2017.

I've no idea how I can get my missing tabs back, and as they weren't the most recent in my search history, it would probably be quicker to start afresh.