Is the 165 Hz refresh rate useful outside gaming?

Mostly for games and PC input. Films and TV shows are mastered at lower frame rates, so the high refresh mainly smooths motion and reduces tearing with VRR on consoles and graphics cards.

How does it compare with Samsung's QD-OLED models?

QD-OLED sets generally push higher brightness and richer color volume. This OLED set trades some of that for deep blacks and wide viewing angles, and its 165 Hz panel is aimed at fast motion.

Do I need to worry about burn-in?

OLED panels can retain static images over long periods. Vary content, avoid leaving news tickers or game HUDs on for hours, and use the TV's screen-care settings.

A 65-inch screen is about 57 inches wide, so plan for a stand or wall space wider than that and a viewing distance of roughly 8 to 10 feet for 4K detail.

What do I need for 4K at 165 Hz?

A source that supports high refresh over HDMI 2.1, such as a recent console or PC, plus a certified HDMI 2.1 cable. Check that VRR is enabled in the source settings.