There are various topics on the subject with sometimes many replies that make it hard to find useful instructions.

One important point of note is that this process assumes the crash was due to something that didn't corrupt the previous session files, and that they still exist in the relevant folder.

Here I would like to record the steps that I took to restore my many, many, many open tabs.

1. Without closing Opera after the crash Open the sessions folder for your user profile
   The opera://about page will tell you the location of your user profile. Go there in Explorer and then look in the Sessions folder.
   For me it was in C:\Users\Juan\AppData\Roaming\Opera Software\Opera GX Stable\Sessions.
   If you caught the crash in time you should see at least 2 versions each of a Sessions_[timestamp] and Tabs_[timestamp] file.

2. Take note of the various timestamps, they should correspond between each pair of files
   In my case the following files are what I see after completing this restoration process, but initially there were 2 files each, one pair with the timestamp 13300879778116338 and expected larger file sizes (9 065 KB & 465 KB) and the other pair with the timestamp 13300889583051312, which were the new session files created after the crash and each in the region of 10's to 100's of KB small.
   
   I also took the precaution of copying the older files to another folder, just in case...

3. Open Windows Registry Editor
   Press Win+R and run regedit.exe
   Navigate to Computer\HKEY_CURRENT_USER\Software\Opera Software
   
   Take note of the Stable Last Running Time timestamp.
   The number I saw at the time was bigger than the crashed session's 13300879778116338 and smaller than the new session's 13300889583051312

4. Rename the old files with the newer timestamps.
   Close Opera.
   Select the newer Session file, press F2 to edit the file name, copy the name with the newer timestamp to clipboard.
   Delete the newer file.
   Press F2 and rename the older Session file with the newer value in the clipboard.
   Repeat with the Tabs file.

5. Open Opera and hope for the best!

Renaming the older files from before the crash to the timestamp of the new files after the crash meant that Opera saw my files as being newer than when it crashed, and it then opened all my old windows and tabs like nothing had happened.

Good luck!

@hellffer Check the sessions folder and see if there are files there like I mentioned. If I remember correctly my instructions were from opening opera again after the crash, where it made new session files but didn't delete the older ones. Sorry if that wasn't clear. Good luck !

@hellffer Check the sessions folder and see if there are files there like I mentioned. If I remember correctly my instructions were from opening opera again after the crash, where it made new session files but didn't delete the older ones. Sorry if that wasn't clear. Good luck !

There are various topics on the subject with sometimes many replies that make it hard to find useful instructions.

One important point of note is that this process assumes the crash was due to something that didn't corrupt the previous session files, and that they still exist in the relevant folder.

Here I would like to record the steps that I took to restore my many, many, many open tabs.

1. Without closing Opera after the crash Open the sessions folder for your user profile
   The opera://about page will tell you the location of your user profile. Go there in Explorer and then look in the Sessions folder.
   For me it was in C:\Users\Juan\AppData\Roaming\Opera Software\Opera GX Stable\Sessions.
   If you caught the crash in time you should see at least 2 versions each of a Sessions_[timestamp] and Tabs_[timestamp] file.

2. Take note of the various timestamps, they should correspond between each pair of files
   In my case the following files are what I see after completing this restoration process, but initially there were 2 files each, one pair with the timestamp 13300879778116338 and expected larger file sizes (9 065 KB & 465 KB) and the other pair with the timestamp 13300889583051312, which were the new session files created after the crash and each in the region of 10's to 100's of KB small.
   
   I also took the precaution of copying the older files to another folder, just in case...

3. Open Windows Registry Editor
   Press Win+R and run regedit.exe
   Navigate to Computer\HKEY_CURRENT_USER\Software\Opera Software
   
   Take note of the Stable Last Running Time timestamp.
   The number I saw at the time was bigger than the crashed session's 13300879778116338 and smaller than the new session's 13300889583051312

4. Rename the old files with the newer timestamps.
   Close Opera.
   Select the newer Session file, press F2 to edit the file name, copy the name with the newer timestamp to clipboard.
   Delete the newer file.
   Press F2 and rename the older Session file with the newer value in the clipboard.
   Repeat with the Tabs file.

5. Open Opera and hope for the best!

Renaming the older files from before the crash to the timestamp of the new files after the crash meant that Opera saw my files as being newer than when it crashed, and it then opened all my old windows and tabs like nothing had happened.

Good luck!