@leocg

Of course you have to pin a few tabs in Opera in a workspace (have several of them) Several normal tabs must be pinned in the same work area. You then take out one of these normal tabs with the mouse so that it becomes an opera window in its own right.
4th Then you first close the Opera window in which the pinned tabs are available. Then you close the Opera browser where only one tab has been pulled out as a new browser window All browser windows / instances are now closed When you restart Opera, the pinned tabs are no longer there

I guess, that depends on the setting "Keep tabs from previous session".
Since the last session didn't have any pinned tabs, he probably just took it over.

Best wishes
Waldemar