Composer 1 vs. 2

In VSCode, both Composer 1 and Composer 2 are currently available. Composer 2 can be run as composer in the terminal, whereas Composer 2 is available as composer1.

How to let Composer install a version that is not stable, but rather alpha

Run these two commands

composer config minimum-stability alpha
composer config prefer-stable true

The first one allows installing alpha packages. Available options (in order of stability) are dev, alpha, beta, RC, and stable.

The second one instructs Composer to prefer stable packages when they are available.

More details here: https://getcomposer.org/doc/04-schema.md#minimum-stability

How to run Composer with unlimited memory

Set the shell environment variable COMPOSER_MEMORY_LIMIT to -1:

COMPOSER_MEMORY_LIMIT=-1 composer install <PACKAGE>