pecl multiple php version
pecl install mcrypt
pecl/mcrypt is already installed and is the same as the released version 1.0.3
install failed

update-alternatives –config=php
update-alternatives –config=php-config
update-alternatives –config=phpize

pecl install -f pecl

Also can help config-set:
pecl config-set ext_dir /usr/lib/php/20201226
pecl config-set php_bin /usr/bin/php7.4
pecl config-set php_ini /etc/php/7.4/cli/php.ini
pear config-set ext_dir /usr/lib/php/20201226
pear config-set php_bin /usr/bin/php7.4