Syntax errors on 4.0.0-alpha6

I just updated from 4.0.0-alpha5 to -alpha6, and ran into syntax errors on my Drupal 9.5.11 site.

Some examples:

ParseError: syntax error, unexpected 'protected' (T_PROTECTED), expecting variable (T_VARIABLE) in /code/web/modules/composer/conditional_fields/src/Form/ConditionalFieldDeleteForm.php on line 47

ParseError: syntax error, unexpected ')', expecting variable (T_VARIABLE) in /code/web/modules/composer/conditional_fields/src/Form/ConditionalFieldEditForm.php on line 42 #0 /code/vendor/composer/ClassLoader.php(427): Composer\Autoload\{closure}('/code/web/modul...')

Made some adjustments to fix it on my end. Will upload patch shortly.