You really need to start with a whole new profile. Goto the URL opera://about, take note of the "profile" path, fully exit Opera via menu -> exit, and rename the profile folder so that Opera creates a new one. The profile folder is hidden by default so you'll have to unhide it (show hidden items in Finder or whatever file manager you use).

Before you close Opera, goto the URL opera://settings/passwords, click the 3 dots to the right of "saved passwords", and export your passwords to a csv file. Open the csv file in a text editor to confirm they're there.

To save open tabs, right-click a tab, goto "save", and choose "all tabs to a speed dial folder". Repeat for each extra workspace if you use workspaces.

To export bookmarks, goto the URL opera://bookmarks and use the drop-down at the bottom left.

Once you rename Opera's profile folder and start Opera, you can goto the URL opera://settings/importData, choose "Bookmarks HTML file" in the drop-down, and import your bookmarks HTML file that you export earlier. Then, you can goto the URL opera://bookmarks and move the imported bookmarks to where they're supposed to be.

Then, right-click on the speed dial folder that represents your opened tabs and choose "open all in tabs". If you use workspaces, create/edit your workspaces again and then right-click on the speed dial folder that represents the open tabs for each extra workspace and choose to open all the tabs in the corresponding workspace.

To import passwords, goto the URL opera://flags/#password-import, make sure the import flag is enabled, restart Opera if you have to enable it, goto the URL opera://settings/passwords, click the 3 dots to the right of "saved passwords" and choose to import your passwords csv file. Just keep this issue and workaround in mind.

If you use Opera Sync, you'll want to wipe out your data at https://www.sync.opera.com/ by choosing "reset passphrase" before signing into your Opera account in the new profile and turning on Sync again. Also, it might be a good idea to avoid syncing settings.

Once you get everything working right, you can reinstall your extensions, readjust your extension settings, and readjust Opera's settings.

I do not suggest trying to transfer over history and cookies to the new profile.