Dynamically define dropdown list in custom Power BI visual

Thank you, dm-p, after checking your code I was able to implement the same!

Much appreciated for your help, you rock!

I confirm, I checked in power bi, and power bi desktop, the contents of the dropdown change dynamically, the contents can be loaded from other methods of other classes, which made my life much easier.

barChartSettingsModel.ts

import powerbiVisualsApi from "powerbi-visuals-api";
import { formattingSettings } from "powerbi-visuals-utils-formattingmodel";
class positionSelect {
   private po : powerbi.IEnumMember[];
   setPosition():powerbi.IEnumMember[]{
    this.po = [];
    let min = Math.ceil(1);
    let max = Math.floor(10);
    let nm =  Math.floor(Math.random() * (max - min + 1)) + min;
    for (let i = 1; i<= nm ; i++){
        let curPositionOptions: powerbi.IEnumMember = {value : i, displayName : i.toString()};
        this.po.push(curPositionOptions);    
    }
    return this.po
   }
}
let positionOptions : powerbi.IEnumMember[];
class LabelsCardSetting extends formattingSettings.SimpleCard {
    name: string = "labels"; // same as capabilities object name
    displayName: string = "Labels";
    public option: formattingSettings.ItemDropdown;
    public setOption():formattingSettings.ItemDropdown {
    positionOptions = new positionSelect().setPosition();
    this.option = new formattingSettings.ItemDropdown({
        name: "option", // same as capabilities property name
        displayName: "Option",
        items: positionOptions,
        value: positionOptions[0] 
    });
    return this.option
    }
    public slices: formattingSettings.Slice[] = [ this.setOption()];
}
/**
* BarChart formatting settings model class
*/
export class BarChartSettingsModel extends Model {
    labels = new LabelsCardSetting();
    cards: Card[] = [this.labels];
}

capabilities.json

"labels": {
      "properties": {
        "option": {
          "type": {
            "enumeration": []
          }
        }
      }
    },