Can't change screen refresh rate on M1 MBP

Discussion in 'Installation and Configuration of Parallels Desktop' started by insanityfarm, Nov 5, 2021.

  1. insanityfarm

    insanityfarm Bit poster

    I set up my first Windows VM on my new M1 Max MBP the other day, and for better compatibility with old games I went searching for a way to lock the VM's screen refresh rate at 60Hz. I was unable to do this anywhere in Windows settings, in every place I know to look 120Hz was the only option available. I read somewhere that Parallels just passes the host refresh rate through to the guest OS, so I tried lowering it in macOS System Preferences.

    Weirdly, even with the Mac at the lower rate Windows continued to run (or at least reported it was running, I didn't confirm) at 120Hz, even after I restarted the VM, relaunched Parallels, and rebooted my Mac. So I reverted the Mac refresh rate to "ProMotion" (120Hz) and rolled back to a VM snapshot I'd taken before beginning this process.

    What surprised me was that once I did that, Windows was locked to a refresh rate of 60Hz! I have no idea how or why. Unfortunately, now I don't have a way to put it back the way it was. I confirmed my settings in System Preferences and rebooted the Mac. Windows reports that "Generic PnP Monitor and Parallels Display Adapter (WDDM)" only support 60Hz now. When I created this snapshot it was still 120Hz, and I have no earlier snapshot to roll back to. It looks like it's stuck like this.

    Full disclosure: Before lowering the macOS refresh rate, I'd been experimenting with Custom Resolution Utility inside the VM. I don't really understand what that tool does or how it works. I was careful to create my snapshot before messing with it, so I could roll back if anything went awry. It didn't appear to work at all; after all my changes Windows still reported 120Hz. Then I went did the stuff I described above. Is it possible that CRU made a change to the VM that persisted after snapshot rollback? Or is that a red herring?

    Can anyone help me get my VM to use 120Hz again? Bonus points if you know of a way to toggle between refresh rates at will, for those old games that need it.
  2. insanityfarm

    insanityfarm Bit poster

    I just found this knowledge base article which says Windows settings in the VM will always show 60Hz on a 120Hz screen, but that's not actually correct. At least not in Windows 11. Just to confirm I'm not imagining things, I spun up a new W11 VM and took a screenshot (attached) of the "120 Hertz" option. That's the only option available, but it's gone from my original VM, replaced with "60 Hertz" only.

    Is there a way to reset the adapter or something, to revert back to its initial state? Or should I just ignore this (like the KB says) because Windows is actually using the correct refresh rate and just misreporting it?

    Attached Files:

  3. Egehan

    Egehan Bit poster

    Hey, I recently faced the same issue you had.
    I was using an external display at 60Hz, but before that, I installed Win10 via the Parallels Desktop 18 on my M1 Pro device. I am pretty sure it was first 120Hz after I installed Parallels Tools as well.

    Now it went back to 60Hz, and I had no solution for that. What I did to resolve is this, you can try as well:

    - First, if the Windows10 (Parallels) is in fullscreen mode, make it window mode and check the screen refresh rate on the windows settings. It should be now 120Hz.
    - If this does not solve the problem, reinstall Parallels Toolbox at this step. After the Windows restart, check the FPS again.
    - If this does not solve the problem as well, just go to the Display adapter properties and select "Disable this device" option, the Parallels should be in windowed mode at this time. Then reinstall the Parallels Toolbox again and restart the Windows. Check the FPS again, it should be 120Hz. At the end, make it back to fullscreen mode.

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