At RNO Avis is doing "Contactless Returns" due to COVID. That means there is no return agent (probably laid them off) present so you drop keys in a drop box and leave the car. Good luck with any support. I am glad I learned of this through someone else so I did not trouble myself with a car rental from them a couple weeks ago as I was tempted to do.

Did you file a case with the corporate customer service noting you returned the car? If it isn't checked in properly, at some point in the next couple days, Avis will send you a certified letter demanding the car back.