You can definitely upgrade manually. The main part is to change your composer.json to allow CakePHP 4.4 to be installed via e.g. using "cakephp/cakephp": "4.4.*" as a version string
Also enabling debug mode and setting
'Error' => [
'errorLevel' => E_ALL,
]
in your config/app.php helps you show verbose error messages.
The rest is basically following the errors or deprecation warnings displayed on your page and fix them accordingly.
4.4 Migration Guide - 4.x has a list of most if not all deprecations and changes which have happend.
your command indicates that you are running 8.2 but something along the way seems to have changed that. Can’t say why because this heavily depends on your server config.
your other warning PHP Warning: Unsupported declare 'strict_types' also indicates a PHP Version < 7.0 because declare(strict_types=1) was added in PHP 7.0