In \Drupal\project_browser\Element\ProjectBrowser::getDrupalSettings the variable $source, which is provided as a string, gets replaced with a ProjectBrowserSourceInterface object. Later, that variable is used to compare it with a string. This will never produce the expected result.
Enable the recipe source and xdebug line 132 in \Drupal\project_browser\Element\ProjectBrowser, you will see that an object gets compared with the string recipe.
Do not override the variable with a different type, PhpStan will complain about that anyway. Use a different variable instead.
Active
2.0
Code
This problem is fixed by 🐛 WSOD when using settings to limit sources to recipes Active , so let's focus our efforts there.