We had a similar experience a week ago, also a ChargePoint. In our case, the charger was no longer charging, the R1T said to disconnect, but the charger was still powered up and thought it was charging. So it wouldn't release the lock in the handle. Rivian support said to call them and ask them to power it down. They said they couldn't do that, only reboot. So they rebooted. In the reboot process it seemed to briefly power off twice, and that was enough to release the lock so I could pull the handle out. As OP stated, manual release in the vehicle did nothing.
Good to know! I cannot say I've had a bad experience, but did watch a lot of MacGyver back in the day. There is always a pocket knife and duct tape within reach.