@levelev Okay so for everyone who stumbles upon this thread. I found a solution. It is by no means a good solution, but as a last resort it at least works.
So to get the old "Session_[number]" and "Tabs_[number]" file, I used the program "GetDataBack Pro". It is a data recovery program. In case you accidentally delete your partition or your harddrive gets corrupted somehow, it can be used to restore data. This program costs money, so be aware of that. Other data recovery programs probably also work, but I can't confirm. I already own a copy of GetDataBack Pro, so I thought I'll just try if it can find something. And indeed it found multiple older "Session_[number]" and "Tabs_[number]" files. Some weeks old and some just 1 or 2 days. I used the most recent one that still had a big file size. Unfortunately I couldn't get Opera to use this older file instead of newer ones. So I opened the "Session_[number]" file (in my case it is was called Session_13252992390325014) with Notepad++, copied the whole text with all the random symbols and pasted it into this website: https://www.convertcsv.com/url-extractor.htm and it gave me a list of all the URLs that are between those random symbols. With that list I could then use this extension: https://chrome.google.com/webstore/detail/open-multiple-urls/oifijhaokejakekmnjmphonojcfkpbbh to load that list of URLs into Opera as tabs. If you do that, I would recommend to check the "Dont load tabs until selected" checkbox, to make sure Opera does not crash again from the load.
Step by step:
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Go to the the URL "opera://about" in your Opera browser.
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Scroll down a bit and take note of the profile path and navigate there via the windows explorer.
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Find the "Sessions" folder. In there should be 4 files called:
Session_[very long number]
Session_[very long, but slightly higher number]
Tabs_[very long number]
Tabs_[very long, but slightly higher number]
You want the "Session_[number]" file with the slightly lower number. It will be the older file. -
Open that file with "Notepad++" or another text editor that can read it. There will be a lot of random symbols in it. But somewhere between these symbols are the URLs of the tabs you lost.
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Copy the entire text and paste it into this website: https://www.convertcsv.com/url-extractor.htm and hit "extract". It will give you a list of the URLs it found in that text.
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Take a quick look in that list and check if those are the websites you are looking for.
If those are NOT the websites you lost, you will have to use a data recovery software to get an older version of the "Session_[number]" file back.
I can confirm "GetDataBack Pro" works and it found multiple older deleted versions. Some from 1 or 2 days ago, some from 1 or 2 weeks ago. Do a deep scan and make sure to check all partitions it can find on the harddrive you selected. It also works if you are using a SSD instead of a HDD. Copy all older versions of the "Session_[number]" you can find to a save location, open and do step 5 until you think those are the websites you are looking for. -
Install this extension: https://chrome.google.com/webstore/detail/open-multiple-urls/oifijhaokejakekmnjmphonojcfkpbbh and use it to open that list of URLs as new tabs. I would recommend to check the "Don't load tabs until selected" checkbox, to make sure Opera does not crash again from the load.
TIPS:
If one URL does not load or does look wrong, that could be because "convertcsv.com" thought a letter or word behind the URL in that large text file was part of this URL. It only happened a few times in hundreds of tabs for me, but it could be different for you. Try to delete the last character, or the last few characters of the URL and see if that takes you to the side you are looking for.
Hope that helps someone!
If someone finds an easier solution for some of these steps, please reply.
Oh and make sure you use Sessions Buddy (https://chrome.google.com/webstore/detail/session-buddy/edacconmaakjimmfgnblocblbcdcpbko) or a similar extension to make sure this does not happen again.
