-I'm aware that it's supposed to be Opera, so it can't be completely different, but maybe just a different UI change. I'm thinking the tool bar on the top right. I like how you can press next to the extension button and it will hide it but I would like to add more there to have a more minimilistic feel.
-I would also like dark mode, as others do too
-More changes for backround, like making it transparent of some sort. On Safari, you can make your start page wallpaper semi-transparent so you can see your desktop, which would be a feature I'd really enjoy, and maybe a theme color change too.