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I just bought myself a 14" MacBook Pro (M1 Pro), which I use as my personal computer, including for casually playing League of Legends (a popular MOBA game).

I am connected to an external display (LG UltraFine 4K 24MD4KL-B) and some external peripherals (mouse, keyboard).

League of Legends runs via Rosetta 2 on Apple Silicon macs, and runs perfectly fine on the built-in display. I run into some issues, however, when connecting my external display: input lag, screen stutter/flaky pixels/glitchy display (I can provide a video to illustrate).

The weird thing is, disconnecting and reconnecting the thunderbolt cable once in-game solves the issue: display becomes pristine, there's no discernible input lag, everything works perfectly. However, this workaround causes the OS to malfunction post-game: application switching no longer works, and subsequent games load into a black screen. A restart solves the issue (but it means I have to restart my machine after every game).

This is kind of a frustrating issue, so I wonder if anyone has faced a similar problem or knows of a potential fix? Also, I don't know which part of the chain is to blame in this: the game itself? macOS Monterey? Rosetta 2? I want to push for an investigation, but I don't want to go barking up the wrong tree.

Full specs:

  • 2021 14" MacBook Pro (M1 Pro, 16GB, 1TB)
  • LG UltraFine 4K 24MD4KL-B
  • External peripherals
  • macOS Monterey 12.0.1 (21A559)

Thanks in advance for any help!

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Welp, I've found the solution by myself!

For anyone who runs into this issue in the future: you have to run the game in Borderless mode (Options > Video > Window mode).

Game runs smooth as butter now :)

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I just received my 14" with M1 Max and quickly tested League of Legends. I tried different settings, Window mode: Borderless seems to be working best together with Wait for vertical sync: Disabled but it's still not 100% fluid.

I have a 34" LG ultrawide connected via TB3.

My previous setup was a 15" MBP i9 with eGPU via TB 3 (RX Vega 64) connected via DisplayPort and the game was 100% fluid even in full screen mode.

I have a feeling there is something weird going on with the TB3 connection. I will try to connect the monitor via HDMI to see if that makes it better.

Would be curious to see if there are other people experiencing this.

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  • Thanks for the feedback! Out of curiosity, what settings are you running the game at? I would assume the M1 Max can handle everything at the highest level, but I wanted to be sure. Also, are the fluidity issues related to display glitchiness like what I described, or more standard frame drops/lower framerate? Nov 2 '21 at 9:58
  • Today I tested also with the HDMI cable directly connected and no difference. I'm running the game at very high max settings, it's super fluid and no frame drops/stuttering on internal monitor, even with v-sync activated. On the external monitor 3440x1440 unfortunately I tried every setting but still does a bit of stuttering :(
    – mtt
    Nov 2 '21 at 20:43
  • Ah that sucks :( LoL runs non-natively, so maybe it is an unfortunate reality that it might not run 100% smoothly at max settings on a 1440p ultrawide display. Does the stuttering stop if you reduce the quality to High for instance? Nov 3 '21 at 9:11
  • That's something I need to test but on the internal monitor works flawlessly with ~100FPS at max details with 2048x1200 I think to remember so not far away from the external monitor resolution, but I'll give it a try ! :D
    – mtt
    Nov 3 '21 at 10:31
  • @KarimNassar out of curiosity with your 4k display what level of detail are you using and what FPS do you see?
    – mtt
    Nov 3 '21 at 10:32

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