While running phpbbcli.php like described in https://www.phpbb.com/support/docs/en/3.3/kb/article/phpbb-32%2B-text-reparser/ to enable / disable an extension like e.g.

php bin/phpbbcli.php extension:disable my/extension 

the following errors where showing up in my PHP error logs: 

[10-Apr-2020 15:59:51 Europe/Berlin] PHP Fatal error: APCuIterator::__construct(): APC must be enabled to use APCuIterator in /var/www/phpbb/cache/driver/apcu.php on line 32

[10-Apr-2020 17:29:55 Europe/Berlin] PHP Fatal error: APCuIterator::__construct(): APC must be enabled to use APCuIterator in /var/www/phpbb/cache/driver/apcu.php on line 32

Additionally the following feedback on disabling / enabling the extension is missing:

[OK] Successfully disabled extension my/extension

[OK] Successfully enabled extension my/extension

If i'm understanding the message correctly this is originating from having APCu configured for phpBB and from the default of PHP / APCu not enabling APCu for the CLI version of PHP:

https://www.php.net/manual/en/apcu.configuration.php#ini.apcu.enable-cli

While setting apc.enable_cli to 1 would hide this message the manual linked above is saying that this should mostly be done for testing and debugging purposes.

Instead of requiring to have this functionality enabled phpBB could disable the usage of APCu for phpbbcli.php completely (PHP_SAPI === 'cli').