Hello readerintrouble,
The only way you can recover iCloud Tabs that you’ve accidentally closed via Safari on your Mac is to have a backup of your data via Time Machine on the day you closed the iCloud Tabs.
If you have a Time Machine backup of your Mac that you’ll like to restore from, the link below will show you how to do that.
Recover files using Time Machine and Spotlight on Mac - Apple Support
1) On your Mac, open a Finder window, then type a search word or phrase in the search field in the upper-right corner.
2) Refine the results by specifying search criteria using the search bar.
3) Click the Time Machine icon
in the menu bar, then choose Enter Time Machine.
If the Time Machine icon isn’t in the menu bar, choose Apple menu
> System Preferences, click Time Machine
, then select “Show Time Machine in menu bar.”
4) Use the arrows and timeline to browse the Time Machine backups.
5) Select one or more items you want to restore (these can include folders or your entire disk), then click Restore.
Restored items return to their original location. For example, if an item was in the Documents folder, it’s returned to the Documents folder.
Please keep in mind that restoring from a Time Machine backup will revert all data on your Mac back to the time and date associated with the backup you restored from.
Post back if you still have problems after working through the steps in the link above.
Thanks for using the Apple Support Communities.
Cheers!