I checked some other forums and reddit threads. If the above troubleshooting doesn't work, then there's the possibility that the AVR has gone bad.
https://www.avsforum.com/threads/a-v-receiver-not-nearly-as-loud-anymore.2936944/(check Peterc613's comment; the other forums I checked all say what he says)
I don't like throwing money on repairs when it's a significant fraction of a replacement model, but it's not like your model is obsolete even 5 years later. I'm willing to live with the inconvenience as long as it's still working.
