iMac M1 (2021) – Screen Flickering & Heat After macOS 15.3 Update

Hi, I’m using a 24-inch iMac M1 (2021, 16GB RAM), purchased in November 2021. This is the first issue I’ve encountered since owning it, and it started only after updating to macOS 15.3 (on January 30), continuing in macOS 15.4.

I’ve been experiencing serious screen flickering issues, which began right after updating to macOS 15.3 and continue in macOS 15.4. Initially, screen flickering would start after 1–2 hours of use, especially in warmer conditions. A long horizontal black line also appeared permanently near the top-right of the screen. The device would heat up during these incidents, though not always to an extreme level after the first few occurrences. However, on April 25, the issue worsened significantly. The screen no longer flickers in the same way, but now the entire upper half of the screen is covered in multiple lines, and the top-right corner of the device has become extremely hot to the touch. I’m now using SwitchResX to disable the iMac’s internal display and continue working via an external monitor (BenQ EW3270U) as a temporary workaround.