How do I prioritize game performance over browser performance when using Opera GX?

How do I make Opera GX use less resources when a game is running, so my game runs smoothly?

I want to change the "reopen closed tab" shortcut in Opera on Linux to Ctrl+Shift+T, like in other browsers. How do I do this?

My Opera start page is cluttered with unwanted news and old speed dials. I want to:

-Remove irrelevant news feeds.
-Change/remove outdated speed dials.
-Add quick access to work email and frequently used sites.
-Have a cleaner, more minimalist look.

How do I customize it step-by-step?

@leocg Opera One

Opera's taking ages to launch. Specifically, the start page loads slowly, and it freezes for a few seconds. I recently added extensions and keep many tabs open.

How do I customize startup to load faster without losing pinned tabs or having to re-login to sites?

Opera's acting up: websites are displaying old info (like a news headline from yesterday), I keep getting logged out of my email, and videos buffer constantly. I've heard clearing cache/cookies helps, but I'm not sure how.

How do I clear them safely? What's the difference, and will I lose saved passwords?