I think you're saying that you have 120V AC at the circuit breakers. I saw you said you checked receptacles for 120V AC, but you didn't say whether they were getting power.
So let me assume that none of the 12V DC lights or devices are working, either inside or outside. The battery is dead. The furnace and air conditioner and thermostat are dead. the water heater (if Suburban) works on 120V AC, but not on propane/12V DC.
And your microwave may be fried for some reason.
If that's all correct, I would say you either had a power surge/lightning strike/incorrectly wired 30 amp pedestal. The high voltage fried both your microwave and the Power Converter board in your power center.
While on shore power, the Power Converter takes in 120V AC and outputs 12V DC to the fuses and to the battery to keep it charged. If that's all working, when you disconnect from shore power, the battery supplies power to the fuses so lights and other things work.
You might find our
Electrical User Guide helpful. It's more oriented toward 50 amp electrical service, but the principles are the same.