Driver's side taillights stopped working

If this is just the left rear assembly then we need to check the connector on the inside of the assembly and make sure it is connected. If this is ok, we need to operate the lamps and check for power on each wire. I included the wiring diagram for your reference.

If this all checks out then it could be a BCM issue. Clearly we don't want to go there first but they are known to fail for different issues like this.

Let me know what you find and we can go from there.

https://www.2carpros.com/articles/how-to-check-wiring