M1 MacBook Air 2020 - Screen randomly turns on/off with external USB-C monitor (Sequoia 26.6.1)

Question

M1 MacBook Air 2020 - Screen randomly turns on/off with external USB-C monitor (Sequoia 26.6.1)

I'm experiencing a strange issue with my M1 MacBook Air (2020) running macOS Sequoia 26.6.1. The MacBook screen randomly turns on and off (dimly) every couple of minutes, but ONLY when an external monitor is connected via USB-C.

Details:

- Issue occurs exclusively with external USB-C monitor connected (tested with LG and Dell monitors)

- Happens every few minutes, seemingly random with no light changes in the room

- Does NOT occur without external monitor

- Does NOT occur with HDMI adapter + monitor

- Already tried: f.lux uninstall, NVRAM/PRAM reset, AutomaticBrightness disabled

- ioreg output shows erratic AmbientBrightness values, but disabling ALS didn't resolve it

The issue started after recent macOS updates and persists across multiple monitors and connection types. It's clearly related to the USB-C external display handling, not a hardware failure (screen works fine without monitor).

Attached: ioreg -l | grep -i brightness output for reference.

Has anyone experienced this? Any suggestions before contacting Apple Support?

ioreg -l | grep -i brightness

Publicado el 18/08/2026 07:23 a.m.

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Answer 1

crazyalf

Nivel 4

2.427 puntos

18/08/2026 05:05 p.m. en respuesta a oscardemiguel

Buenas noches oscardemiguel

Lo primero de todo, Gracias por visitar la Comunidad de soporte de Apple en español.

Tengo yo un MacBook Pro M1 de 2020. También le conecto un monitor externo Dell U2412M a través de USB-C, y no tengo esos problemas. Cuando he conectado un segundo monitor a través de un hub con HDMI (usando InstantView recomendado por el hub), tampoco he tenido esos fallos.

Particularmente no uso f.lux.

¿Has probado a crear un perfil nuevo de usuario en tu Mac y comprobar que funciona bien tus pantallas externas? Por si hubiera algún problema en tu perfil.

Un saludo

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