@NatureWithGreenWorld You would need to have a backup of the "Sessions" folder in the profile folder (profile path shown at the URL opera://about) from the time your tabs were still there. If you have a backup like that, you can delete everything in your current "Sessions" folder and copy over the files from the backup "Sessions" folder.
Or, see https://forums.opera.com/post/406843 for how you can extract the open tabs from backed-up session files and open them back up.