Thread size the exactly the same for every water heater in North America, including a lot of the commercial heaters. That’s 3/4-inch, inside diameter.
That heater is a power-vent model, so it has a blower housing on top. The anode is just on the edge of it, toward the center of the tank, but the housing may overlap a trifle.
It would be informative to know how old your electric is and how much is left of the anode. Sometimes, sacrificial anodes get used up very fast in softened water, but not always.
You don’t have to worry about clearance if you switch anodes before the tank is installed. If you’re going to switch to magnesium, I’d suggest SKU33. That’s the same size anode as the manufacturers use for their 12-year-warranty heaters. It might be necessary to unscrew the housing to make the switch, if the housing overlaps the anode port too much.
After that, I’d check the anode every couple of years, if possible, to see how fast it’s being consumed, and switch to a powered anode if the wear rate is too rapid, and if that overlap issue will permit it.
The fuel source has no bearing on anode issues.