Hi Marcos,
Yes, that definitely sounds like the source of the issue. The error is telling you that you are missing a PHP extension - php-curl. If you follow the recommended installation instructions, this PHP extension is installed at this step:
However, PHP 8 introduces a number of backwards incompatible changes and
AtoM 2.7 does not currently support PHP8. Per
this announcement from the Maintainers, the team intends to upgrade AtoM's PHP support in the 2.9 release.
Your best bet will be to downgrade your PHP version in Ubuntu 20.04 to 7.4, and make sure that php7.4-curl (along with all the other PHP extensions) is properly installed before continuing.
Good luck!