USB charging is not a practical way to power the SX740 HS while recording. Based on the guide and user reports, the camera charges too slowly over micro-USB to keep up with video power draw, so you should not expect to record indefinitely from USB power alone.

For continuous external power, the workable solution mentioned is a Canon-compatible AC adapter/dummy battery kit (such as the ACK-DC110 style mentioned by a user). That replaces the battery with a dummy coupler and powers the camera from mains, which can let the camera run much longer.

However, there is still an important limitation: community feedback notes a maximum video recording time of about 30 minutes per clip. So even with AC power, you likely won’t get a single uninterrupted 2-hour 4K file in-camera. You may need to restart recording, or use HDMI output for longer external capture/streaming if that fits your setup.

Also note that battery life estimates vary: one answer cites roughly 60 minutes CIPA and about 100 minutes movie recording under some conditions, so actual runtime depends on settings and use.