This documentation is not using the current rendering mechanism and is probably outdated. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
Installation for both TYPO3 CMS installation types (manual/composer) are supported. For both a compatible installation is provided.
Download the extension recaptcha either with the browser from typo3.org or github and upload it into the installation in the admin tools extensions, or directly in the admin tools extensions with the integrated search.
On the console in the folder where the project composer.json resides just type:
composer require evoweb/recaptcha ^8.2 composer update
After the extension is installed by either way you always need to activate it. Normally this is done in the admin tools extensions. But its also possible to activate it via console:
$ ./bin/typo3 extensionmanager:extension:install recaptcha
If, the captcha should be usable in backend context or you like to have a default configuration without touching TypoScript, the extensions need to be configured in the admin tools extensions. Via the cog as shown on the screenshot.