Now, if Sync isn't working for you and you can still load the old Opera on the old computer, you can do exporting and importing:

In Opera on the old computer, goto the URL opera://bookmarks and use the drop-down at the bottom left to export your bookmarks to an HTML file. Then, copy that HTML file to a USB stick for example to transfer it to the new computer. Then, in Opera on the new computer, goto the URL opera://settings/importData, select "Bookmarks HTML file" in the drop-down and point it to the bookmarks HTML file to import your bookmarks. Then, goto the URL opera://bookmarks and go in to the "Bookmarks Bar" folder to find your imported bookmarks. You can then move the bookmarks to where you want. For example, you can move imported speed dials to the "Speed Dial" folder and imported bookmarks to the root of the "Bookmarks Bar" folder or "Other Bookmarks". How ever you want.

For passwords, in the old Opera, goto the URL opera://password-manager/settings and export your passwords to a CSV file. Then, open up the CSV file in a text editor to make sure the passwords are actually there. Then, in Opera on the new computer, goto opera://password-manager/settings and import the CSV file from the old Opera.

For open tabs, before you export your bookmarks, in each workspace, in each window, right-click on an open tab, goto "Save" and choose "all tabs to a speed dial folder". You can then name those speed dial folders "Window 1 - Workspace name1", "Window 1 - Workspace Name2", "Window 2 - Workspace Name 1" etc. so you know what tabs are for what workspace. Then, in the new Opera, after creating the same workspaces and number of windows, in each workspace, in each window, you can right-click on its corresponding imported speed dial folder and choose "open all in tabs" to restore your open tabs. This does not restore navigation history for each tab though.

For history, you can goto the URL opera://about, take note of the "profile" path, close Opera and copy the "History" file in the profile folder over to the new computer and use that copy to replace the existing one in Opera's profile folder.

For extensions, you reinstall them. For cookies, you don't transfer those. You just log in to sites again in the new Opera. For settings, you just adjust your settings again.

For autofill form data and a few other things, you might be able to copy the "Web Data" file in the profile folder for the old Opera and use it to replace the "Web Data" file for the new Opera. Might not work properly though if anything in the "Web Data" file is encrypted by the old Opera where the new Opera can't read it. But, you can try. If it doesn't work, you can just delete the "Web data" file to have Opera create a fresh one that it can write to again.