Diagnosis
That's a side effect of how the Mini-LED local dimming zones work. When a very bright object is on a dark background, the zones around it can't turn off completely, creating a halo or blooming effect. This is normal to some degree, but can often be improved.
How to Fix It
Dive into the picture settings. 1) While watching your problematic content, press the settings button on the remote. 2) Go to Picture > Advanced Settings. 3) Look for "Local Contrast" or "Micro Contrast." Try setting it to "High" or "On." 4) Find the "Backlight" or "Local Dimming" setting itself. Experiment with different modes—sometimes "High" can reduce blooming compared to "Auto," but it can also crush black detail. It's a trade-off.
If That Didn't Work
The effect is most noticeable in a pitch-black room. Adding some subtle bias lighting behind the TV (an LED strip) can trick your eyes and make the blooming far less apparent.
Heads Up
This is a physical limitation of any full-array local dimming (FALD) TV, including Mini-LED. No setting will eliminate it entirely, only minimize it. Content mastered for OLEDs will always show this more.