Can't remove caldav account from macOS

Nextcloud version (eg, 20.0.5): 21.0.3
Operating system and version (eg, Ubuntu 20.04): Ubuntu 20.04 (server), macOS Big Sur 11.5.1 (client)
Apache or nginx version (eg, Apache 2.4.25): 2.4.41-4ubuntu3.4
PHP version (eg, 7.4): 7.4.3

The issue you are facing:

Can’t remove caldav account from macOS.

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:
I have a caldav account installed in my Mac clients (a macbook pro and a mac mini). I want to remove it, so I go into System Preferences > Internet Accounts, select the caldav account, and click the - button to remove it. I get a popup saying I’ll need to remove it from all my machines, so I click ‘remove from all’. The account disappears and then about a minute later it reappears in the list.

The output of your Nextcloud log in Admin > Logging: There’s nothing in my admin log related to this.

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

<?php
$CONFIG = array (
  'passwordsalt' => 'passwordsalt',
  'secret' => 'secret',
  'trusted_domains' =>
  array (
    0 => 'localhost',
    1 => 'domains'
  ),
  'datadirectory' => '/path/to/ncdata/',
  'dbtype' => 'pgsql',
  'version' => '21.0.3.1',
  'overwrite.cli.url' => 'https://nextcloud.domain.com/',
  'dbname' => 'nextcloud_db',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'user',
  'dbpassword' => 'password',
  'installed' => true,
  'instanceid' => 'ocjkjc6zbpli',
  'upgrade.disable-web' => 'true',
  'log_type' => 'file',
  'logfile' => '/var/log/nextcloud/nextcloud.log',
  'loglevel' => '2',
  'log.condition' =>
  array (
    'apps' =>
    array (
      0 => 'admin_audit',
    ),
  ),
  'mail_smtpmode' => 'smtp',
  'remember_login_cookie_lifetime' => '7200',
  'log_rotate_size' => '0',
  'trashbin_retention_obligation' => 'auto, 180',
  'versions_retention_obligation' => 'auto, 365',
  'simpleSignUpLink.shown' => false,
  'filelocking.enabled' => true,
  'memcache.distributed' => '\\OC\\Memcache\\Redis',
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'redis' =>
  array (
    'host' => '/var/run/redis/redis-server.sock',
    'port' => 0,
    'timeout' => 0.5,
    'dbindex' => 0,
    'password' => 'password',
  ),
  'logtimezone' => 'America/Los_Angeles',
  'htaccess.RewriteBase' => '/',
  'maintenance' => false,
  'mail_smtpsecure' => 'tls',
  'mail_sendmailmode' => 'smtp',
  'mail_from_address' => 'address',
  'mail_domain' => 'gmail.com',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_smtphost' => 'smtp.gmail.com',
  'mail_smtpport' => '587',
  'mail_smtpname' => 'smtpname',
  'mail_smtppassword' => 'password',
  'overwritehost' => 'nextcloud.domain.com',
  'overwriteprotocol' => 'https',
  'ldapIgnoreNamingRules' => false,
  'ldapProviderFactory' => 'OCA\\User_LDAP\\LDAPProviderFactory',
  'encryption.legacy_format_support' => true,
  'encryption.key_storage_migrated' => false,
  'default_phone_region' => 'us',
  'memcache.local' => '\\OC\\Memcache\\Redis',
);

The output of your Apache/nginx/system log in /var/log/____: I think this is the wrong log, here’s my /var/log/apache2/access.log

::1 - - [28/Jul/2021:02:09:38 -0700] "OPTIONS * HTTP/1.0" 200 132 "-" "Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f (internal dummy connection)"
::1 - - [28/Jul/2021:02:09:55 -0700] "OPTIONS * HTTP/1.0" 200 132 "-" "Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f (internal dummy connection)"
::1 - - [28/Jul/2021:14:07:46 -0700] "OPTIONS * HTTP/1.0" 200 132 "-" "Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f (internal dummy connection)"
::1 - - [28/Jul/2021:16:02:55 -0700] "OPTIONS * HTTP/1.0" 200 132 "-" "Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f (internal dummy connection)"
::1 - - [28/Jul/2021:16:03:58 -0700] "OPTIONS * HTTP/1.0" 200 132 "-" "Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f (internal dummy connection)"
::1 - - [28/Jul/2021:16:04:03 -0700] "OPTIONS * HTTP/1.0" 200 132 "-" "Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f (internal dummy connection)"

All that said, this seems like a MacOS problem. Apple support says to ask here about what to do. Any tips?