Just want to share my succesfull experience from past minutes.
Latest Opera version for Windows desktop. Experienced a sudden crash, followed by an instant restart by Opera, resulting in a lost Session. A session of over 200 tabs was close to be lost.
Such crashes I did not noticed for very long time, last time before the user profile folder structure was reorganized in Opera in 2021.
Happily I managed to recover it.
While Opera it's not closed yet, it's necessary to do a backup of this folder - %AppData%\Opera Software\Opera Stable\Sessions
After closing this empty Opera session, replace the content of current Sessions folder with that from backup, and delete the file Session_########## with the smallest size from those two (only a few bytes). Eventually the smallest Tabs_### file if there are 2 as well. This should do the trick.