It depends on the circumstances. On smooth asphalt, I stand upright in the same way as without a wheel. But, here in Finland, the city does not maintain the cycle paths as much as the carriageway. The cycle paths have a lot of potholes and bumps from tree roots. So on complex surfaces, I bend my knees a little. My maximum speed is 25 km/h, although the Tesla can be driven at a higher speed.
Ride safe out there!