Beginning June 2024, authentication to UPS APIs using access keys will be deprecated in favor of an OAuth 2.0 security model. All new and existing API integrations must migrate to the OAuth 2.0 to continue to access the APIs. View the OAuth Migration Guide for more details on the impacts to your API integration with UPS.
We have some readymade magento 2 extensions to solve shipping issues with new Rest API token flow integration.
https://www.ecomplugins.com/magento2/magento2-ups-extensions
Magento Marketplace Link
https://commercemarketplace.adobe.com/partner/EcomPlugins