Hiya Onikushu and welcome.
There is little true comparison between how we make mead in 2020 and how mead was likely made 1000 or 1500 years ago. How was honey harvested before we had modern hives? How many bees were boiled in the must? How much wax was scooped out when the must boiled? How potable was the water that was used? What flowers did the bees feed on? From where was the yeasts that were used? From the honey itself? From stirring rods? From wooden or clay pots? How was the mead stored? How likely was the mead that was made, made without the addition of volunteer bacteria and fungi? How long was fermentation permitted to take before the mead was drunk?
My guess is that the "Vikings" - insofar as we know their history and we are not simply mythologizing their culture as most folk in the US are wont to do - often used psychotropic herbs in their meads to add to its narcotizing effects but then before the advent of hops in beer, ale was often made with similar herbs (gruit).
You want to make a mead that will have 3% alcohol? Dissolve a scant 11.5 oz of honey in a gallon of water and ferment that dry. It won't have much flavor and it won't have much alcohol but if you trap enough of the CO2 it will be carbonated and if you monitor the process you might call it macaroni while there is still some unfermented sugar so you will have a sweet-ish, carbonated low ABV mead. No Viking is around to argue with you that what you've made ain't the real thing...