Here is a possible work around! https://www.opera.com/computer/portable

For open tabs, you can right-click the a tab and choose "save all tabs as a speed dial folder".

For bookmarks, you can goto the URL opera://bookmarks and export them to an HTML file using the drow-down at the bottom left. Since speed dials are bookmarks, they'll be backed up to.

For passwords, you can goto the URL opera://settings/passwords and click the kebab menu (3 vertical dots) to the right of "saved passwords" to export them as a csv file.

Then, once you start over and enable sync, you can import your bookmarks using the drop-down at the bottom left of opera://bookmarks. You can then right-click on the speed dial folder and choose "open all in tabs". Then, for passwords, you can goto the URL opera://flags/#PasswordImport, enable the flag, restart Opera and import the CSV file via the same menu you used to export at opera://settings/passwords.

Before doing all that, you can do a test. Download the Opera installer, launch it, click "options", set "install path" to a folder named "Opera Test" on your desktop, set "install for" to "standalone installation", uncheck "import data from default browser", and install. Test in that Opera first without enabling Opera Sync. If it works fine and doesn't crash, then enable Opera Sync. If it starts crashing, it's something with Opera Sync (perhaps corrupted data and you should probably wipe out everything like suggested above). If it doesn't start crashing after you enable Opera sync, just wiping out your data fro Opera desktop might be enough.

Of course, Opera shouldn't crash no matter what, and it should be something Opera should fix where you don't have to do anything, but the above might be the only way at the moment.

Have uninstalled and reinstalled

When uninstalling, did you also choose to delete your data so that you start with a fresh profile? If so, are you using Opera Sync?