I note it is locked and just cannot figure out how it is installed. I’ve done sudo dnf list installed | grep voikko but it did not return anything. So this leads me to believe that the extension has a different package name or it was installed through the Libreoffice extensions store. However, I’ve searched there and saw nothing of consequence installed.
That makes it a bit weirder since I don’t seem to have any Voikko package installed. If you note in the screenshot, all three extensions have a lock beside them, which seems to suggest that they are locked and need to be removed via elevated permissions. The problem is that I could not find any package installed on my system that points to Voikko.
LibreOffice extensions don’t need to be shipped as RPM packages. You could, for instance, download them from LibreOffice’s extensions page, and install them from the Extensions menu.
That should mean it didn’t come bundled with LibreOffice. Which of the three options selected individually displays it? If it only gets displayed with Installed for all users, then that could be the reason for not being possible to remove it (installed by another user maybe).
For testing purposes I have installed the said extension, and it gets displayed for Installed for current user. Afterwards I could uninstall it.