Example how to implement Infinite Scroll in Xamarin.Forms applications. - http://julianocustodio.com/listview-infinite-scroll

MainViewModel.cs

        public MainViewModel()
        {
            Items = new InfiniteScrollCollection<string>
            {
                OnLoadMore = async () =>
                {
                    IsBusy = true;

                    // Ler a proxima pagina
                    var page = Items.Count / PageSize;

                    //Busca os itens
                    var items = await _service.GetPessoasAsync(page, PageSize);

                    IsBusy = false;

                    // Itens que serão adicionados
                    return items;
                }
            };

            Download();
        }

        public bool IsBusy
        {
            get => _isBusy;
            set
            {
                _isBusy = value;
                OnPropertyChanged();
            }
        }