main()
const main = async () =>{
const task = await Task.findById('614ac31e103d9c5329d38686')
await task.populate('owner').execPopulate()
console.log(task.owner)
}
execPopulate() is not a function
From changelogs at https://mongoosejs.com/docs/migrating_to_6.html#removed-execpopulate,
the line should be replaced to
await task.populate('owner')