While that's a common misconception, it doesn't have to be the same version and it usually isn't.
Most web hosts have multiple PHP versions installed at the same time. The typical setup we see in 2020 includes PHP 5.6, 7.0, 7.1, 7.2, 7.3 and 7.4. Versions 5.6, 7.0 and 7.1 are end of life but are provided as a means for older sites which do not support newer PHP versions to continue function for a while until they can be upgraded.
The PHP version to be used by the web server for your site is selected in the hosting control panel. Depending on the server setup this either modifies your site's .htaccess file or, more rarely, the server configuration for your site. This means that your site can run on a different PHP version than the default PHP CLI version.
/usr/bin/php typically refers to the default PHP version which in most cases is the oldest available version. Newer versions have different paths. We typically see paths like /usr/local/bin/php74 or /usr/bin/ea-php74. The exact path to the PHP 7.4 CLI binary depends on the server setup, that's why the Schedule Automatic Backups page of our software and our documentation says that you need to ask your host for it.
Also note that due to the very limited information you provided your problem may be something different entirely. You say that you saw the "unsupported authorisation Protocol" error in your crontab. First of all, your crontab only includes the commands to run and when to run them. It is not a log. So I had to guess that you are talking about a CRON error log. Second, the message "unsupported authorisation Protocol" with that bad grammar and capitalization is not something that MySQL or PHP outputs. I guess it's translated from German. The only thing I could use was an inference. MySQL 8 uses by default an authentication scheme that's incompatible with older PHP versions. You use PHP 7.4 in the site which is very new and does support it. But on the CLI you are using /usr/bin/php which is the default PHP version of the server and chances are it's an old version that doesn't speak MySQL 8's authentication protocol. That's why I am asking you to check that first. It's an educated guess based on the incomplete information I was given.