upgrading from 8x1.7 to 2alpha7 I get WSOD syntax error, unexpected '|'

I am having this issue as well and it is blocking me from updating to Drupal 10

I got this same error as well. Had to rollback the update to 2.0.0-alpha3 for now.

I am unable to reproduce this error. Can someone who's seeing the error, provide more details such as drupal version, etc.

This error is thrown in versions of php < 8 . The error is due to the use of union types in the property declarations:

public string|array $block_config;
public string|array $menu_config;

This means $block_config and $menu_config can be either a string or an array but will throw an error in php v < 8.0 since unions are not supported