CTRL not working correctly with VoiceOver

[WestonThayer]

VoiceOver is MacOS's built-in screen reader (System Preferences > Accessibility > VoiceOver). When enabled, it announces UI elements currently focused on the screen. You normally interact with it via a huge suite of keyboard shortcuts.

A very important shortcut is simply hitting CTRL (the Control key, keysym 0xffe3) to silence VoiceOver. I can't seem to get this working with OSXvnc server.

I've tried the following combinations:

• User server mode
  • Keyboard Layout: U.S.
    • Keyboard Events: Hardware Events + Event Source: Private Event Source
    • Keyboard Events: Hardware Events + Event Source: HID Event Source
    • Keyboard Events: Hardware Events + Event Source: 10.3 API (No Source)
    • Keyboard Events: User Session Events + Event Source: Private Event Source
    • Keyboard Events: User Session Events + Event Source: 10.3 API (No Source)
  • Keyboard Layout: Unicode Hex Input
    • Keyboard Events: Hardware Events + Event Source: HID Event Source
    • Keyboard Events: Hardware Events + Event Source: 10.3 API (No Source)
  • Keyboard Layout: Current Keyboard
    • Keyboard Events: Hardware Events + Event Source: HID Event Source
    • Keyboard Events: Hardware Events + Event Source: 10.3 API (No Source)
• System server mode
  • Keyboard Layout: U.S.
    • Keyboard Events: Hardware Events + Event Source: 10.3 API (No Source)

I can see the CTRL key lighting up in System Preferences > Accessibility > Accessibility Keyboard, and https://keycode.info shows the right key events. Any ideas?

More details:

• OS: Big Sur 11.4
• VNC viewer: MacOS's built in, tried others as well
• OSXvnc version: https://github.com/stweil/OSXvnc/releases/tag/V5_3_0

It works correctly with MacOS's built-in VNC server (Apple Remote Desktop, ARD) as well as RealVNC server.

[stweil]

Can someone confirm this issue and help to find a solution?