Routes Error after upgrade to v4.5.5

1. CI4 does not use Guzzle at all.
2. The error is clearly caused by Guzzle.

Why do you think it's having problems finding a route in CI4?

When you upgrade CI4, you must read the upgrading guides:
https://www.codeigniter.com/user_guide/i...ading.html
Did you read them, and followed the  instructions?

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper