@Stoffbeuteluwe autoplay is a new restriction in the browsers… you have to click on something… dumb for a mirror with no mouse!!

fix

edit the smart-mirror/main.js
find the line

let mainWindow

and change it so it looks like this

let mainWindow; function createWindow() { app.commandLine.appendSwitch('autoplay-policy', 'no-user-gesture-required'); //< -------- added

then save and restart MM