Had the same problem

https://www.python-ldap.org/en/python-ldap-3.3.0/reference/ldap.html?highlight=cacert#tls-options

libldap does not materialize all TLS settings immediately. You must use OPT_X_TLS_NEWCTX with value 0 to instruct libldap to apply pending TLS settings and create a new internal TLS context

This solved for me.