@leocg I apologize. I wasn't thinking and clicked on a link that mentioned dark mode for Opera without taking the time to read it fully.

I was able to update the Opera GX Browser to LVL 6 (core: 114.0.5282.106), and when I select dark mode, it stays on dark mode even when I close and reopen it. Thank you, developers, and I’m sorry for anyone still experiencing issues. I genuinely sympathize with those who continue to struggle with this problem.