luetage said :

Saving sessions is not an option currently, but you can get this functionality by installing an extension.

Sidebar: https://addons.opera.com/en/extensions/details/v7-sessions/?display=en

Regular: https://addons.opera.com/en/extensions/details/tabhamster/?display=en

Naming these extensions as "session manager" is a fraud, a cheat, a swindle, an embezzlement !!!!

These extensions only store the current address of each tab and LOSSES the HISTORY of each TAB.

A session is NOT a collection of bookmarks.

A session IS the collection of the HISTORY of each TAB.

These extensions do not what they promise !!!
These extensions are pale counterfeits, forgeries, piracies !!!