Starting Django on Docker Alpine Results in django.db.utils.OperationalError: (2000, 'Unknown MySQL error')

Alpine 3.12, django 3.1, mysqlclient 2.0.1

When running python3 ./manage.py runserver 8080,

 File "/usr/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
 return self.cursor.execute(sql, params)
 File "/usr/lib/python3.8/site-packages/django/db/backends/mysql/base.py", line 73, in execute
 return self.cursor.execute(query, args)
 File "/usr/lib/python3.8/site-packages/MySQLdb/cursors.py", line 206, in execute
 res = self._query(query)
 File "/usr/lib/python3.8/site-packages/MySQLdb/cursors.py", line 319, in _query
 db.query(q)
 File "/usr/lib/python3.8/site-packages/MySQLdb/connections.py", line 259, in query
 _mysql.connection.query(self, query)
django.db.utils.OperationalError: (2000, 'Unknown MySQL error')

The above error occurred.

The settings are

DATABASES = {
  'default': {
　　  'ENGINE': 'django.db.backends.mysql',
  　　'NAME': '*****',
 　　 'USER': '*****',
  　　'PASSWORD': '*****',
 　　 'HOST': '*****',
  　　'PORT': '3306',
  　　'OPTIONS': {
    　　'charset': 'utf8mb4',
  　　},
  },
}

With this configuration,

the error (2000, 'Unknown MySQL error') occurs when 'charset': 'utf8mb4' is included in the OPTIONS.

When this setting is removed or changed to utf8, the error does not occur.

The detailed cause is unknown.