After hours of endless googling, I have the solution! In order to achieve this, I needed validRange and visibleRange with custom date specifications. With my case being unique of start = CURRENT YEAR and end = YEAR AFTER, Here's what I did.
var startOfYear = new Date(new Date().getFullYear(), 0, 1).toISOString().slice(0, 10);
var startOfNextYear = new Date(new Date().getFullYear() + 2, 0, 1).toISOString().slice(0, 10);
initialView: 'multiMonthYear',
visibleRange: function() {
return {
start: startOfYear,
end: startOfNextYear,
};
},
validRange: function() {
return {
start: startOfYear,
end: startOfNextYear,
};
},
Hopefully that helps someone. Spent HOURS looking for this.