You're not confused. You're expecting the tank monitors to work as advertised.
Your black and grey tanks are showing empty. Your fresh water is showing full. And your propane is almost empty.
From my experience, today's OEM tank monitors work no better than those of 20 years ago.
We've owned a new 3051S for 9 months and the grey and black tank monitors have never been accurate.
We keep up with the amount of grey water we use but if you miscalculate it will come up through the shower drain. Don't store anything on the shower floor that water will ruin.
Our black tank monitor always showed empty from the first day. It never showed a level even when full until we rinsed the tank 3 or 4 times with using the tank rinsing set-up.
We also had an idea of how many times we had flushed and you can always look at the tank level thru the toilet to be certain.
The fresh water tank so far has been accurate. After sanitizing the tank and flushing all the fresh water lines I dumped it and added back 14 gallons. The monitor showed 33% full so I trust it.
The blue line shows your fresh tank is full. If no one filled it the check valve in your water pump may be leaking by and filling your tank. If it over fills, water will run out of the vent at the fill port.
Be sure your water pump is off when using city water.
Drain your fresh water tank. My drain is inside a rear compartment on the passenger side with the water filter. When empty, the monitor should show empty. If it fills again on its own your pumps check valve isn't working.
If this is the case, turning off the city water supply and running the pump some may fix the problem.
You never want to drive on the highway with all your tanks full as you will most certainly be overweight. I run with approximately 10 gallons fresh, black and grey empty.
I'm sure others will chime in a about this.
There are after market tank level devices but I'm not familiar with them, their installation or cost.
On a side note, it appears you are on shore power since your water heater is on electric.
Your batteries are only showing 12.8 volts. That is about as low as the voltage should ever be.
When on shore power, mine usually shows 13.2 to 14.1, depending on the charging mode.
I'd suggest checking the water level in your coach batteries and filling them to the proper level with distilled water only.
If they don't need water and you feel they are being charged you may want to get them tested under load. You don't want them to die on you.
Enjoy your RV! It is quite a learning experience but we wouldn't want to travel any other way.
2017 Forester 3051S