You can still install the Opera version of FVD Speed Dial by dragging the nex file to opera://extensions if you have it. I found it on archive.org. It won't override the start page anymore, but you can still get to it via the extension's button or by using the URL chrome-extension://pncpfofkienlinhfknpmgjnjhdoclfhh/newtab.html.
The problem with the Opera version though was that it was always out of date compared to the Chrome version. The Opera version was basically a modified version of an old build of the Chrome version that used a different way to override the start page since the way the Chrome version does it has always been blocked by Opera.
Now that even the Opera version can't override the start page (like the Chrome version), and the Opera version is no longer present on addons.opera.com, you might as well just goto the Chrome web store and install the Chrome version (when you have https://addons.opera.com/en/extensions/details/install-chrome-extensions/ installed). Then, you'll get the latest version of the extension that you could never get with the Opera version. It of course won't be able to override the start page, but you can get to it via the extension button or the URL chrome-extension://llaficoajjainaijghjlofdfmbjpebpa/newtab.html. You can use the latter with the "open specific pages" startup option too if you want.
The downside to both though is that left-clicking won't work on the FVD Speed Dial page anymore in Opera. You'll have to right-click a dial and choose "open in new tab". To work around that, you have to go in the extension's settings and change clicking to open in a new tab. Then, left-clicking will at least work that way.
Of course, there's not much point in doing any of that since it doesn't replace the start page anymore.
