LEDs light on very little current, so a trickle that an old bulb ignored shows up as a faint glow after the switch is off. That glow is called ghosting.
Usual sources: a smart switch or dimmer with no neutral, powering itself through the lamp; a lighted locator switch; or voltage induced where a long run sits beside live conductors. Practical fixes are a switch that uses a neutral, the bypass the switch maker specifies, a plain unlit switch, or a lamp that maker lists as compatible.
If the switch is landed on the neutral instead of the hot, the fixture stays energized when it looks off. That is a shock hazard. Turn the breaker off and call a licensed electrician.