2015 Subaru Outback with 50,000 km, the brake feels very hard when starting the car, but it's normal after starting. What could be the reason?

It's normal for the brake pump to start working after the engine is started.

It's fine, it's normal. Mine had it too, I just ignored it.

Check if there are any minor leaks in the vacuum booster hose.

This is normal. The braking system relies on the battery to function.

You might still be stepping on the brake after turning off the power when parking.

That depends on how long the interval is between the two starts. If it's within a day, the vacuum should be fully maintained. Otherwise, there might be a slight vacuum leak in the vacuum booster system. Ideally, the vacuum should hold for a long time, at least a day without any issues.

Delay caused by the power assist system.

Replace the vacuum tube.

The car won't start, and there's no brake assist!

When the vehicle is not started, the brake system doesn't have power assistance, so the brake pedal feels hard to press. However, once the vehicle is started, vacuum assistance kicks in, making the brake pedal feel softer.