Flicker is one of the few electrical symptoms you can narrow down surprisingly well from the sofa, because the pattern of what flickers and when points fairly directly at the cause.
Start with how much of the house does it
A single fixture that flickers is almost always the lamp, the holder, or a dimmer that isn’t compatible with the LED you installed. A whole room points at a loose connection in that circuit, usually at a switch or the first outlet in the run. The entire house dimming in step with a motor starting — a fridge, a pump, an air conditioner — points at the service connection or the main panel, and that’s the version to take seriously.
Why LEDs made this more common
Incandescent bulbs had enough thermal inertia to hide small voltage dips. LEDs respond in milliseconds, so a fluctuation that was invisible ten years ago is now perfectly obvious. Pair a dimmer designed for resistive loads with a driver that expects something else and flicker is close to guaranteed even though nothing is actually faulty.
The version that’s genuinely urgent
Flicker together with warmth at a switch plate, a faint ozone or fishy smell, or browning around an outlet means a connection is arcing. Arcing makes heat inside a wall cavity where nothing is watching it. That’s a same-day call, not a weekend project.