switch php versions on Ubuntu PHP
YourPC://$ sudo update-alternatives --config php

There are 3 choices for the alternative php (providing /usr/bin/php).

  Selection    Path             Priority   Status
* 0            /usr/bin/php8.1   81        auto mode
  1            /usr/bin/php7.4   74        manual mode
  2            /usr/bin/php8.0   80        manual mode
  3            /usr/bin/php8.1   81        manual mode

Press <enter> to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/bin/php7.4 to provide /usr/bin/php (php) in manual mode

YourPC://$ php -v
PHP 7.4.3 (cli) (built: Mar  2 2022 15:36:52) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
    with Zend OPcache v7.4.3, Copyright (c), by Zend Technologies
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