Hemorrhoids wroteNot sure what OLED you had,I have an old Samsung KE55 since 2013, mostly used for watching TV, ~8 hours a day, if I lower the brightness to minimum in a pitch dark room with a grey color background picture test, thats the only way I see a barely visible shadow of local news logos, small price to pay to many when it comes to overall picture quality (no blur for gamers), especially movies at night, no visible black bars (backlight) at 21:9 with the lights off, and SDR looks similar to cheap HDR on oled in some scenes.
The KE55 is an old full hd OLED tv with no HDR support at all. HDR 10 is panel dependable & requires at least 1000 nits of brightness. The C9 is amuch advance OLED panel that has
HDR Real Scene Peak Brightness @ 726 cd/m²
HDR Peak 2% Window @ 855 cd/m²
HDR Peak 10% Window @ 845 cd/m²
Source: Rtings.com
OLEDs detecting HDR sources and increasing their brightness to these levels for a solid HDR experience , are highly susceptible for image retentions / burn Ins. The enemy of organic light emitting diode panels is high brightness. As HDR is gaining unprecedented momentum in gaming / movies , C9 being a home entertaining unit with a 3k investment for the 65" makes it at a risk position. This is also applies to any high end OLED models from different brands too ( Sony A9G for example).