Assuming localhost, with self-signed certs, and server config

[mysqld]
bind-address = 127.0.0.1
mysqlx-bind-address = 127.0.0.1
require_secure_transport = ON

this works

import pymysql
import ssl

ctx = ssl.create_default_context()
ctx.check_hostname = False
ctx.verify_mode = ssl.VerifyMode.CERT_NONE

conn = pymysql.connect(user='root', host='127.0.0.1', ssl=ctx)

Obviously you can elide the disabling of verification if your certs are signed by a public CA.

Appending

cursor = conn.cursor()
cursor.execute("SHOW SESSION STATUS LIKE 'Ssl_cipher';")
for row in cursor:
    print(row)

gives the following when I tested

('Ssl_cipher', 'TLS_AES_256_GCM_SHA384')

This seems to me that the documentation for the ssl parameter needs updating

I'd also been wondering about this for a number of months

Ok. A shorter working example. Not sure if if violates some knowledge of the internals, but this works as at writing.

import pymysql
conn = pymysql.connect(user='root', host='127.0.0.1', ssl={"verify_mode": None})

or any non-empty dict really

For the documenting of ssl taking an SSLContext, #1045 has been merged.
I forgot to mention this issue in there when opened that PR, 😅 , but hopefully that will help others in future.