When I use arrow functions, the context of count is accesible, and it works:

class Counter {
    count = 0
    constructor({
        countElementId, 
        incrementElementId, 
        decrementElementId
    }){
        
        this.countElement = document.getElementById(countElementId)
        this.incrementElement = document.getElementById(incrementElementId)
        this.decrementElement = document.getElementById(decrementElementId)
        
        this.incrementElement.addEventListener("click", () => this.incrementCount())
        this.decrementElement.addEventListener("click", () => this.decrementCount())
    }

    incrementCount(){
        
        this.countElement.innerText = ++this.count
    }

    decrementCount(){
        this.countElement.innerText = --this.count
    }
}

function main () {
    const peopleCounter = new Counter({
        countElementId: "count-el",
        incrementElementId : "increment-btn",
        decrementElementId: "decrement-btn"
    })
}

main() 

But count stops being accessible when I change it this way in the constructor:

this.incrementElement.addEventListener("click", this.incrementCount)
this.decrementElement.addEventListener("click", this.decrementCount)