create table events (
    id integer primary key,
    name text not null,
    event_date text not null check (
      -- YYYY-MM-DD
      event_date glob '[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]'
      and date(event_date) is not null
      and date(event_date) = event_date
    )
  );

In Python that raises this error if the date is invalid:

  sqlite3.IntegrityError: CHECK constraint failed:
    event_date glob '[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]'

Storing dates as INTEGER (year * 10000 + month * 100 + day, e.g. 20260530) is not so bad. Proper date / timestamp types would be great though.