Some of the new ones need to have their filters dusted, which is a change from the past. And Rheems, if the FVIR device is triggered, shut down and the device has to be replaced before the heater will work again.
Anodes can be hard to remove. There is a Tanklet about that in the Troubleshooting section. Impact wrenches usually work. I really think you’re going to find that you have anode left when you check. It varies all over the place, but as long as you’re not using a softener, odds are your anodes still have a year or three left on them.
You can post a picture of them here, if you like, and we’ll tell you what we think.