iphone 8 plus cantbget sounds on alerts

The first thing to check is the ring/silent switch on the side of the phone. That is obvious but also something frequently overlooked.

I was not referring to the volume -- I was referring to the ring/silent switch which is above the volume controls on the left side of the phone.

You're not the first and I'm sure won't be the last. I've accidentally done it myself. Glad that worked.