I would bet that electricity demand goes up, not down. When a good becomes cheaper/more efficient, demand increases.
2. Demand is up in this scenario, not supply, because of all the things being electrified.
But there isn't any real reason to think this is implied under a "high renewable" scenario.
In-fact, some of efficiency gains are probably driven by increased costs.
The improved efficiency needs to be more than the drop in marginal cost which is what governs demand, nothing to do with how much more electricity you use today. And even then, that relationship isn't linear because a 30% reduction in cost can drive a 60% increase in demand because that reduction puts it in a new price bracket where a lot more people can afford it (since wealth is non-linear). This stuff is super non trivial and has all sorts of higher order effects.