It looks like Drupal 10.1.0-beta1 rc1 updated the dependency version of 'guzzlehttp/promises' from 1.5 to 2.0.
Unfortunately, 'aws/aws-sdk-php' used by some modules is not compatible with 'guzzlehttp/promises’ 2.0, and this blocks the update to 10.1 stable (10.1-alpha does install).
The AWS SDK devs have acknowledged the issue, but it will not be addressed until at least August.
https://github.com/aws/aws-sdk-php/issues/2713
Promises 2.0 was just released a month ago on May 21st, so it would be nice to drop this version requirement to provide other components time to update.
