This is a quick and dirty POC to show how it can be achieve to create dynamically generated entity. The end code will not look at all like this

dynamically-generated-mikro-entity.ts

function buildEntity(entityName: string, properties: [{ name: string, type: string, columnType: string, index?: boolean }]) {
  class DMLEntity {
    [key: string]: any
    
    constructor() {
      for (const property of properties) {
        this[property.name] = undefined
      }
    }
  }

  Object.defineProperty(DMLEntity,'name', {
    get : function () {
      return upperCaseFirst(entityName);
    }
  });

  const tableName = camelToSnakeCase(entityName)

  for (const property of properties) {
    if (property.index) {
      const index = createPsqlIndexStatementHelper({
        tableName,
        columns: property.name,
      })

      index.MikroORMIndex()(DMLEntity.prototype, property.name)
    }

    Property({
      type: property.type,
      columnType: property.columnType,
    })(DMLEntity.prototype, property.name)
  }

  return Entity({ tableName })(DMLEntity)
}

const Currency = buildEntity("currency", [{
  name: 'code',
  type: 'string',
  columnType: 'text',
  index: true,
}])

const metadata = MetadataStorage.getMetadataFromDecorator(Currency);

console.log(Currency)
console.log(new Currency())
console.log(metadata)

/*
[class Currency]
Currency { code: undefined }
EntityMetadata {
  propertyOrder: Map(0) {},
  properties: {
    code: {
      reference: 'scalar',
        type: 'string',
        columnType: 'text',
        name: 'code',
        getter: false,
        setter: false
    }
  },
  props: [],
    primaryKeys: [],
    filters: {},
  hooks: {},
  indexes: [
    {
      name: 'IDX_currency_code',
      expression: 'CREATE INDEX IF NOT EXISTS "IDX_currency_code" ON "currency" (code)',
      properties: 'code'
    }
  ],
    uniques: [],
    checks: [],
    referencingProperties: [],
    concurrencyCheckKeys: Set(0) {},
  className: 'Currency',
    path: 'Currency',
    collection: 'currency',
    class: [class Currency],
    name: 'Currency'
}
*/