What happens to my trades if the trading platform goes down?

It depends on where your orders live. Orders resting at the broker — GTC profit targets and stop-losses — keep working even if the platform is offline, because the broker holds them. Signals that require the platform to fire (a Monday-open entry, a time-based exit) would be missed during an outage and should be re-evaluated when service resumes. This is why well-built platforms push protective exits down to the broker as real resting orders rather than watching prices themselves, and why your positions and cash are always safe regardless: they live at your brokerage, not the platform. Ask any platform which exits rest at the broker versus which depend on the platform being awake.