AddNewTeamMate.cs

...
namespace In2TeamsSplitter.ViewModels
{
    class TeamMatesViewModel : INotifyPropertyChanged
    {
        ...
        public TeamMatesViewModel()
        {
            AddNewTeamMateCommand = new Command(() => AddNewTeamMate());
            ...    
        }

        public Command AddNewTeamMateCommand { get; }
        
        private void AddNewTeamMate()
        {
            try
            {
                if (string.IsNullOrEmpty(AddName)) throw new Exception("Valid name required");

                int _ = conn.Insert(new TeamMateItem { Name = AddName, Level = AddLevel });
                TeamMateSquad.Add(new TeamMateItem { Name = AddName, Level = AddLevel });

                AddName = string.Empty;
                AddLevel = uint.MinValue;
            }
            catch (Exception ex)
            {
                Application.Current.MainPage.DisplayAlert("error", $"Failed to add {AddName}. Error: {ex.Message}", "Ok");
            }
        }

        ...
    }
}