Import a date from CSV to Date field
You need to convert source date from d-m-Y to Y-m-d

process:
  field_date:
    plugin: format_date
    from_format: 'd-m-Y'
    to_format: 'Y-m-d'
    source: Date


because default field Date use format Y-m-d to store date. and Y-m-d\TH:i:s to store datatime. 

Form display just show default pattern (mm-dd-yyyy) of html5 input date